diff --git "a/ACWing/src/BFS/\347\237\251\351\230\265\350\267\235\347\246\273.java" "b/ACWing/src/BFS/\347\237\251\351\230\265\350\267\235\347\246\273.java"
new file mode 100644
index 0000000000000000000000000000000000000000..30cfedfa8df6b1baeeed3a80fd89cbdde070a3a4
--- /dev/null
+++ "b/ACWing/src/BFS/\347\237\251\351\230\265\350\267\235\347\246\273.java"
@@ -0,0 +1,112 @@
+package BFS;
+
+import java.io.*;
+import java.util.ArrayDeque;
+import java.util.Arrays;
+import java.util.Scanner;
+import java.util.StringTokenizer;
+
+import static java.lang.System.in;
+
+/**
+ * 多源bfs
+ * 173. 矩阵距离
+ * 给定一个N行M列的01矩阵A，A[i][j] 与 A[k][l] 之间的曼哈顿距离定义为：
+ * dist(A[i][j],A[k][l])=|i−k|+|j−l|
+ * 输出一个N行M列的整数矩阵B，其中：
+ * B[i][j]=min1≤x≤N,1≤y≤M,A[x][y]=1dist(A[i][j],A[x][y])
+ * 输入格式
+ * 第一行两个整数n,m。
+ * 接下来一个N行M列的01矩阵，数字之间没有空格。
+ * 输出格式
+ * 一个N行M列的矩阵B，相邻两个整数之间用一个空格隔开。
+ * 数据范围
+ * 1≤N,M≤1000
+ * 输入样例：
+ * 3 4
+ * 0001
+ * 0011
+ * 0110
+ * 输出样例：
+ * 3 2 1 0
+ * 2 1 0 0
+ * 1 0 0 1
+ */
+public class 矩阵距离 {
+    static class node {
+        int x, y;
+
+        public node(int x, int y) {
+            this.x = x;
+            this.y = y;
+        }
+    }
+
+    public static void main(String[] args) throws IOException {
+        Scanner sc = new Scanner(System.in);
+        n = nextInt();
+        m = nextInt();
+
+        for (int i = 0; i < n; i++) {
+                g[i] = next().toCharArray();
+        }
+
+        ArrayDeque<node> q = new ArrayDeque<node>();
+        for (int i = 0; i < n; i++) {
+            Arrays.fill(dis[i], -1);
+            for (int j = 0; j < m; j++) {
+                if (g[i][j] == '1') {
+                    q.add(new node(i, j));
+                    dis[i][j] = 0;
+                }
+            }
+        }
+
+        while (!q.isEmpty()) {
+            node p = q.poll();
+            for (int i = 0; i < 4; i++) {
+                int x = p.x + dir[i][0], y = dir[i][1]+p.y;
+                if (x < 0 || x >= n || y < 0 || y >= m||dis[x][y]!=-1) continue;
+             dis[x][y] = dis[p.x][p.y] + 1;
+                q.add(new node(x, y));
+            }
+        }
+
+        for (int i = 0; i < n; i++) {
+            for (int j = 0; j < m; j++) {
+                bw.write(dis[i][j]+"");
+            }
+            bw.write("\n");
+        }
+        bw.flush();
+
+    }
+
+    static int[][] dir = {{1, 0}, {0, 1}, {-1, 0}, {0, -1}};
+    static int n, m, N = 1010;
+    static char[][] g = new char[N][N];
+    static int[][] dis = new int[N][N];
+    static BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(System.out));
+    static BufferedReader reader = new BufferedReader(new InputStreamReader(in));
+    static StringTokenizer tokenizer = new StringTokenizer("");
+
+    static String nextLine() throws IOException {// 读取下一行字符串
+        return reader.readLine();
+    }
+
+    static String next() throws IOException {// 读取下一个字符串
+        while (!tokenizer.hasMoreTokens()) {
+            //如果没有字符了,就是下一个,使用空格拆分,
+            tokenizer = new StringTokenizer(reader.readLine());
+        }
+        return tokenizer.nextToken();
+    }
+
+    static int nextInt() throws IOException {// 读取下一个int型数值
+        return Integer.parseInt(next());
+    }
+
+    static double nextDouble() throws IOException {// 读取下一个double型数值
+        return Double.parseDouble(next());
+    }
+}
diff --git "a/ACWing/src/DFS/floodfill/\345\237\216\345\240\241\351\227\256\351\242\230.java" "b/ACWing/src/DFS/floodfill/\345\237\216\345\240\241\351\227\256\351\242\230.java"
new file mode 100644
index 0000000000000000000000000000000000000000..8b536af2d306b1f704937454f5664d26a9820601
--- /dev/null
+++ "b/ACWing/src/DFS/floodfill/\345\237\216\345\240\241\351\227\256\351\242\230.java"
@@ -0,0 +1,70 @@
+package DFS.floodfill;
+
+import java.util.ArrayDeque;
+import java.util.Scanner;
+
+/**
+ * https://blog.csdn.net/qq_30277239/article/details/104670312
+ * 显然寻找有多少个四联通块
+ * 并找出最大连通块有多少个
+ */
+public class 城堡问题 {
+    public static void main(String[] args) {
+        Scanner sc = new Scanner(System.in);
+        n = sc.nextInt();
+        m = sc.nextInt();
+        for (int i = 0; i < n; i++) {
+            for (int j = 0; j < m; j++) {
+                g[i][j] = sc.nextInt();
+            }
+        }
+        int cnt = 0, area = 0;
+        for (int i = 0; i < n; i++) {
+            for (int j = 0; j < m; j++) {
+                if (!vis[i][j]) {
+                    area = Math.max(bfs(i, j), area);
+                    cnt++;
+                }
+            }
+        }
+        System.out.println(cnt);
+        System.out.println(area);
+    }
+
+    private static int bfs(int x, int y) {
+        int area = 0;
+        q.clear();
+        q.add(x * m + y);
+        while (!q.isEmpty()) {
+            int p = q.poll();
+            x = p / m;
+            y = p % m;
+            area++;
+            vis[x][y] = true;
+            for (int i = 0; i < 4; i++) {
+                int a = x + dir[i][0], b = y + dir[i][1];
+                if (a < 0 || a >= n || b < 0 || b >= m || vis[a][b]) continue;
+                if ((g[x][y] >> i & 1) == 1) continue;
+                q.add(a * m + b);
+            }
+        }
+        return area;
+    }
+
+    static void dfs(int x, int y) {
+        ans++;
+        vis[x][y] = true;
+        for (int i = 0; i < 4; i++) {
+            int a = x + dir[i][0], b = y + dir[i][1];
+            if (a < 0 || a >= n || b < 0 || b >= m || vis[a][b]) continue;
+            if ((g[x][y] >> i & 1) == 1) continue;
+            dfs(a, b);
+        }
+    }
+
+    static int[][] dir = {{0, -1}, {-1, 0}, {0, 1}, {1, 0}};
+    static int[][] g = new int[51][51];
+    static boolean[][] vis = new boolean[51][51];
+    static ArrayDeque<Integer> q = new ArrayDeque<Integer>();
+    static int n, m, ans;
+}
diff --git "a/ACWing/src/DFS/floodfill/\345\261\261\345\263\260\345\222\214\345\261\261\350\260\267.java" "b/ACWing/src/DFS/floodfill/\345\261\261\345\263\260\345\222\214\345\261\261\350\260\267.java"
new file mode 100644
index 0000000000000000000000000000000000000000..217851f6e020aee7562a40be58916b6975c53753
--- /dev/null
+++ "b/ACWing/src/DFS/floodfill/\345\261\261\345\263\260\345\222\214\345\261\261\350\260\267.java"
@@ -0,0 +1,68 @@
+package DFS.floodfill;
+
+import java.util.ArrayDeque;
+import java.util.Scanner;
+
+/**
+ * https://blog.csdn.net/qq_30277239/article/details/104671983
+ * 显然bfs过程中寻找,
+ * 如果该联通块没有比当前位置数更小的就是山谷
+ * 如果该联通块没有比当前位置数更大的就是山峰
+ * 打上标记,如果都有,则是山坡不计算...
+ */
+public class 山峰和山谷 {
+    public static void main(String[] args) {
+        Scanner sc = new Scanner(System.in);
+        n = sc.nextInt();
+        for (int i = 0; i < n; i++) {
+            for (int j = 0; j < n; j++) {
+                g[i][j] = sc.nextInt();
+            }
+        }
+        int peak = 0, valley = 0;//山峰,山谷
+        for (int i = 0; i < n; i++) {
+            for (int j = 0; j < n; j++) {
+                if (!vis[i][j]) {
+                    High = false;
+                    low = false;
+                    bfs(i, j);
+                    if (!High && !low) ;
+                    else if (!High) peak++;
+                    else if (!low) valley++;
+                }
+            }
+        }
+        System.out.println(peak);
+        System.out.println(valley);
+    }
+
+    static void bfs(int x, int y) {
+        q.add(x * n + y);
+        int t = g[x][y];
+        while (!q.isEmpty()) {
+            int p = q.poll();
+            x = p / n;
+            y = p % n;
+            vis[x][y] = true;
+            for (int i = -1; i < 2; i++) {//八联通
+                for (int j = -1; j < 2; j++) {
+                    if (i == 0 && j == 0) continue;
+                    int a = x + i, b = y + j;
+                    if (a < 0 || a >= n || b < 0 || b >= n) continue;
+                    if (g[x][y] != g[a][b]) {
+                        if (g[a][b] > g[x][y]) High = true;
+                        else if (g[a][b] < g[x][y]) low = true;
+                    } else if (!vis[a][b]) {
+                        q.add(a * n + b);
+                    }
+                }
+            }
+        }
+    }
+
+    static ArrayDeque<Integer> q = new ArrayDeque<Integer>();
+    static boolean High = false, low = false;
+    static int n;
+    static int[][] g = new int[1010][1010];
+    static boolean[][] vis = new boolean[1010][1010];
+}
diff --git "a/ACWing/src/DFS/floodfill/\346\261\240\345\241\230\350\256\241\346\225\260.java" "b/ACWing/src/DFS/floodfill/\346\261\240\345\241\230\350\256\241\346\225\260.java"
new file mode 100644
index 0000000000000000000000000000000000000000..d19d576f5bc3334dffdd92189a274a1ae9eb7e4a
--- /dev/null
+++ "b/ACWing/src/DFS/floodfill/\346\261\240\345\241\230\350\256\241\346\225\260.java"
@@ -0,0 +1,92 @@
+package DFS.floodfill;
+
+import java.util.ArrayDeque;
+import java.util.Scanner;
+
+/**
+ * 农夫约翰有一片 N∗M 的矩形土地。
+ * 最近，由于降雨的原因，部分土地被水淹没了。
+ * 现在用一个字符矩阵来表示他的土地。
+ * 每个单元格内，如果包含雨水，则用”W”表示，如果不含雨水，则用”.”表示。
+ * 现在，约翰想知道他的土地中形成了多少片池塘。
+ * 每组相连的积水单元格集合可以看作是一片池塘。
+ * 每个单元格视为与其上、下、左、右、左上、右上、左下、右下八个邻近单元格相连。
+ * 请你输出共有多少片池塘，即矩阵中共有多少片相连的”W”块。
+ * 输入格式
+ * 第一行包含两个整数 N 和 M。
+ * 接下来 N 行，每行包含 M 个字符，字符为”W”或”.”，用以表示矩形土地的积水状况，字符之间没有空格。
+ * 输出格式
+ * 输出一个整数，表示池塘数目。
+ * 数据范围
+ * 1≤N,M≤1000
+ * 输入样例：
+ * 10 12
+ * W........WW.
+ * .WWW.....WWW
+ * ....WW...WW.
+ * .........WW.
+ * .........W..
+ * ..W......W..
+ * .W.W.....WW.
+ * W.W.W.....W.
+ * .W.W......W.
+ * ..W.......W.
+ * 输出样例：
+ * 3
+ * 求几个八联通块
+ */
+public class 池塘计数 {
+    public static void main(String[] args) {
+        Scanner sc = new Scanner(System.in);
+        n = sc.nextInt();
+        m = sc.nextInt();
+        for (int i = 0; i < n; i++) {
+            g[i] = sc.next().toCharArray();
+        }
+        int ans = 0;
+        for (int i = 0; i < n; i++) {
+            for (int j = 0; j < m; j++) {
+                if (g[i][j] == 'W') {
+                    bfs(i, j);
+                    ans++;
+                }
+            }
+        }
+        System.out.println(ans);
+    }
+
+    static void dfs(int x, int y) {
+        g[x][y] = '.';
+        for (int i = -1; i < 2; i++) {
+            for (int j = -1; j < 2; j++) {
+                if (i == j && j == 0) continue;
+                int a = x + i, b = y + j;
+                if (a < 0 || a >= n || b < 0 || b >= m || g[a][b] == '.') continue;
+                dfs(a, b);
+            }
+        }
+    }
+
+    static void bfs(int x, int y) {
+        ArrayDeque<Integer> q = new ArrayDeque<Integer>();
+        int t = x * m + y;
+        q.add(t);
+        while (!q.isEmpty()) {
+            Integer w = q.poll();
+            x = w / m;
+            y = w % m;
+            g[x][y] = '.';
+            for (int i = -1; i < 2; i++) {
+                for (int j = -1; j < 2; j++) {
+                    if (i == j && j == 0) continue;
+                    int a = x + i, b = y + j;
+                    if (a < 0 || a >= n || b < 0 || b >= m || g[a][b] == '.') continue;
+                    dfs(a, b);
+                }
+            }
+        }
+    }
+
+    static char[][] g = new char[1010][1001];
+    static int n, m;
+}
diff --git "a/ACWing/src/DFS/floodfill/\350\277\267\345\256\253\351\227\256\351\242\230.java" "b/ACWing/src/DFS/floodfill/\350\277\267\345\256\253\351\227\256\351\242\230.java"
new file mode 100644
index 0000000000000000000000000000000000000000..55b8b34b5b686f567ed0b8eafcb9d020eb55e375
--- /dev/null
+++ "b/ACWing/src/DFS/floodfill/\350\277\267\345\256\253\351\227\256\351\242\230.java"
@@ -0,0 +1,58 @@
+package DFS.floodfill;
+
+import java.util.ArrayDeque;
+import java.util.Scanner;
+
+/**
+ * https://blog.csdn.net/qq_30277239/article/details/104672658
+ * 不能使用数字代表方阵坐标,
+ * 只能矩阵坐标
+ * 显然bfs寻路问题,记录路径,从终点往起点走
+ */
+public class 迷宫问题 {
+    static class node {
+        int x, y;
+
+        public node(int x, int y) {
+            this.x = x;
+            this.y = y;
+        }
+    }
+
+    public static void main(String[] args) {
+        Scanner sc = new Scanner(System.in);
+        n = sc.nextInt();
+        for (int i = 1; i <= n; i++) {
+            for (int j = 1; j <= n; j++) {
+                g[i][j] = sc.nextInt();
+            }
+        }
+        ArrayDeque<node> q = new ArrayDeque<node>();
+        int[][] dir = {{1, 0}, {0, 1}, {-1, 0}, {0, -1}};
+        q.add(new node(n - 1, n - 1));
+        int x = 0, y = 0, a, b;
+        while (!q.isEmpty()) {
+            node p = q.poll();
+            vis[p.x][p.y] = true;
+            for (int i = 0; i < 4; i++) {
+                a = dir[i][0] + p.x;
+                b = dir[i][1] + p.y;
+                if (a < 0 || a >= n || b < 0 || b >= n || vis[a][b] || g[a][b] == 1) continue;
+                q.add(new node(a, b));
+                pre[a][b] = p;
+                if (a == 0 && b == 0) break;
+            }
+        }
+        node p = pre[0][0];
+        while (true) {
+            System.out.println(p.x + " " + p.y);
+            if (p.x == n - 1 && p.y == n - 1) break;
+            p = pre[p.x][p.y];
+        }
+    }
+
+    static int n;
+    static boolean[][] vis = new boolean[1010][1010];
+    static node[][] pre = new node[1010][1010];
+    static int[][] g = new int[1010][1010];
+}
diff --git "a/ACWing/src/DFS/\346\234\200\347\237\255\350\267\257/\346\212\223\344\275\217\351\202\243\345\244\264\347\211\233.java" "b/ACWing/src/DFS/\346\234\200\347\237\255\350\267\257/\346\212\223\344\275\217\351\202\243\345\244\264\347\211\233.java"
new file mode 100644
index 0000000000000000000000000000000000000000..53d57ff4bf2f8ff57f426df4c81b58fdee787fb5
--- /dev/null
+++ "b/ACWing/src/DFS/\346\234\200\347\237\255\350\267\257/\346\212\223\344\275\217\351\202\243\345\244\264\347\211\233.java"
@@ -0,0 +1,48 @@
+package DFS.最短路;
+
+import java.util.ArrayDeque;
+import java.util.Arrays;
+import java.util.Scanner;
+
+/**
+ * https://blog.csdn.net/qq_30277239/article/details/104680308
+ * bfs
+ * 显然边界问题
+ * n*2不会超过20w+10
+ * n-1不会低于0
+ * 如果越界则无需记录
+ */
+public class 抓住那头牛 {
+    public static void main(String[] args) {
+        Scanner sc = new Scanner(System.in);
+        n = sc.nextInt();
+        k = sc.nextInt();
+        ArrayDeque<Integer> q = new ArrayDeque<Integer>();
+        Arrays.fill(d, -1);
+        d[n] = 0;
+        q.add(n);
+        while (!q.isEmpty()) {
+            int t = q.poll();
+            if (t == k) {
+                System.out.println(d[t]);
+                break;
+            }
+            if (t + 1 < N && d[t + 1] == -1) {
+                d[t + 1] = d[t] + 1;
+                q.add(t + 1);
+            }
+            if (t - 1 >= 0 && d[t - 1] == -1) {
+                d[t - 1] = d[t] + 1;
+                q.add(t - 1);
+            }
+            if (t * 2 < N && d[t * 2] == -1) {
+                q.add(t * 2);
+                d[t * 2] = d[t] + 1;
+            }
+        }
+    }
+
+    static int N = 201000;
+    static int[] d = new int[N];
+    static int n, k;
+}
diff --git "a/ACWing/src/DFS/\346\234\200\347\237\255\350\267\257/\346\255\246\345\243\253\351\243\216\345\272\246\347\232\204\347\211\233.java" "b/ACWing/src/DFS/\346\234\200\347\237\255\350\267\257/\346\255\246\345\243\253\351\243\216\345\272\246\347\232\204\347\211\233.java"
new file mode 100644
index 0000000000000000000000000000000000000000..f9bbb26dace0e6b433d8d20db7c4fe87caf0b77b
--- /dev/null
+++ "b/ACWing/src/DFS/\346\234\200\347\237\255\350\267\257/\346\255\246\345\243\253\351\243\216\345\272\246\347\232\204\347\211\233.java"
@@ -0,0 +1,53 @@
+package DFS.最短路;
+
+import java.util.ArrayDeque;
+import java.util.Scanner;
+
+/**
+ * https://blog.csdn.net/qq_30277239/article/details/104675982
+ * 马走日bfs寻最短路
+ */
+public class 武士风度的牛 {
+    public static void main(String[] args) {
+        Scanner sc = new Scanner(System.in);
+        m = sc.nextInt();
+        n = sc.nextInt();
+        for (int i = 0; i < n; i++) {
+            g[i] = sc.next().toCharArray();
+        }
+        for (int i = 0; i < n; i++) {
+            for (int j = 0; j < m; j++) {
+                if (g[i][j] == 'K') {
+                    System.out.println(bfs(i, j));
+                }
+            }
+        }
+
+    }
+
+    static int bfs(int x, int y) {
+        ArrayDeque<Integer> q = new ArrayDeque<Integer>();
+        q.add(x * m + y);
+        int a, b;
+        while (!q.isEmpty()) {
+            int p = q.poll();
+            x = p / m;
+            y = p % m;
+            g[x][y] = '*';
+            for (int i = 0; i < 8; i++) {
+                a = x + dir[i][0];
+                b = y + dir[i][1];
+                if (a < 0 || a >= n || b < 0 || b >= m || g[a][b] == '*') continue;
+                if (g[a][b] == 'H') return dis[x][y] + 1;
+                q.add(a * m + b);
+                dis[a][b] = dis[x][y] + 1;
+            }
+        }
+        return -1;
+    }
+
+    static int[][] dir = {{-2, 1}, {-1, 2}, {1, 2}, {2, 1}, {2, -1}, {1, -2}, {-1, -2}, {-2, -1}};
+    static char[][] g = new char[160][160];
+    static int n, m;
+    static int[][] dis = new int[200][200];
+}
diff --git "a/ACWing/src/DFS/\346\234\200\347\237\255\350\267\257/\351\251\254\350\265\260\346\227\245.java" "b/ACWing/src/DFS/\346\234\200\347\237\255\350\267\257/\351\251\254\350\265\260\346\227\245.java"
new file mode 100644
index 0000000000000000000000000000000000000000..528e9093d519e8cd88dc94c04f79c271bb627397
--- /dev/null
+++ "b/ACWing/src/DFS/\346\234\200\347\237\255\350\267\257/\351\251\254\350\265\260\346\227\245.java"
@@ -0,0 +1,48 @@
+package DFS.最短路;
+
+import java.util.Arrays;
+import java.util.Scanner;
+
+/**
+ * 1
+ * 5 4 0 0
+ */
+public class 马走日 {
+    public static void main(String[] args) {
+        Scanner sc = new Scanner(System.in);
+        t = sc.nextInt();
+        while (t-- != 0) {
+            n = sc.nextInt();
+            m = sc.nextInt();
+            x = sc.nextInt();
+            y = sc.nextInt();
+            ans = 0;
+            for (int i = 0; i < vis.length; i++) {
+                Arrays.fill(vis[i], false);
+            }
+            vis[x][y] = true;
+            dfs(x, y, 1);
+            System.out.println(ans);
+        }
+    }
+
+    static void dfs(int x, int y, int cnt) {
+        if (cnt == n * m) {
+            ans++;
+            return;
+        }
+
+        for (int i = 0; i < 8; i++) {
+            int a = x + dir[i][0], b = y + dir[i][1];
+            if (a < 0 || a >= n || b < 0 || b >= m || vis[a][b]) continue;
+            vis[a][b] = true;
+            dfs(a, b, cnt + 1);
+            vis[a][b] = false;
+        }
+    }
+
+    static int t, n, m, x, y, ans;
+    static boolean[][] vis = new boolean[10][10];
+    static int[][] dir = {{-2, 1}, {-1, 2}, {1, 2}, {2, 1}, {2, -1}, {1, -2}, {-1, -2}, {-2, -1}};
+
+}
diff --git "a/ACWing/src/DFS/\346\240\221\347\232\204\351\207\215\345\277\203.java" "b/ACWing/src/DFS/\346\240\221\347\232\204\351\207\215\345\277\203.java"
index 767679cc438b4fc4533ec521e9c36d4fd63f50c0..ad67041a00b470c5260b8815437a073ee5930a67 100644
--- "a/ACWing/src/DFS/\346\240\221\347\232\204\351\207\215\345\277\203.java"
+++ "b/ACWing/src/DFS/\346\240\221\347\232\204\351\207\215\345\277\203.java"
@@ -13,17 +13,20 @@ public class 树的重心 {
             add(a, b);
             add(b, a);
         }
+        vis[1] = 1;
         dfs(1);
         System.out.println(ans);
     }
 
     private static int dfs(int u) {
-        vis[u] = 1;
+
         int size = 0, sum = 0;
         for (int i = he[u]; i != 0; i = ne[i]) {
             int j = e[i];
             if (vis[j] == 1) continue;
+            vis[j] = 1;
             int s = dfs(j);
+            vis[j] = 0;
             size = Math.max(size, s);
             sum += s;//加上孩子节点的个数
         }
@@ -32,7 +35,7 @@ public class 树的重心 {
         return sum + 1;
     }
 
-    static int n, cnt, ans=Integer.MAX_VALUE;
+    static int n, cnt, ans = Integer.MAX_VALUE;
     static int[] he = new int[100100];
     static int[] ne = new int[200100];
     static int[] e = new int[200100];
diff --git "a/ACWing/src/dp/\346\240\221\345\275\242dp/\346\240\221\347\232\204\351\207\215\345\277\203.java" "b/ACWing/src/dp/\346\240\221\345\275\242dp/\346\240\221\347\232\204\351\207\215\345\277\203.java"
index d3fcd7220e7a79a6bc5b34f09e4f97a38589d354..6fe556c916deb8834d661840678ded91d08f47bc 100644
--- "a/ACWing/src/dp/\346\240\221\345\275\242dp/\346\240\221\347\232\204\351\207\215\345\277\203.java"
+++ "b/ACWing/src/dp/\346\240\221\345\275\242dp/\346\240\221\347\232\204\351\207\215\345\277\203.java"
@@ -33,7 +33,7 @@ public class 树的重心 {
     private static int dfs(int u) {
         vis[u] = true;
         int size = 0, sum = 1;
-        //sum为以sum节点为根的子树,节点数量
+        //sum为以u节点为根的子树,节点数量
         for (int i = he[u]; i != 0; i = ne[i]) {
             int j = e[i];
             if (vis[j]) continue;//不用遍历父节点