20190122

TopInterview.md

@@ -26,6 +26,7 @@
 | 033  | [Search in Rotated Sorted Array](https://leetcode.com/problems/search-in-rotated-sorted-array/) |Medium| [Java](./code/lc33.java)
 | 034  | [Search for a Range](https://leetcode.com/problems/search-for-a-range/) |Medium| [Java](./code/lc34.java)
 | 035  | [Search Insert Position](https://leetcode.com/problems/search-insert-position/) |Medium| [Java](./code/lc35.java)
+| 036  |
 | 041  |
 
 
@@ -35,9 +36,10 @@
 | 046  | [Permutations](https://leetcode.com/problems/permutations/)  |Medium| [Java](./code/lc46.java)
 | 048  | [Rotate Image](https://leetcode.com/problems/rotate-image/)  |Medium| [Java](./code/lc48.java)
 | 049  | [Group Anagrams](https://leetcode.com/problems/anagrams/)|Medium| [Java](./code/lc49.java)
+| 050  |
 
 | 053  | [Maximum Subarray](https://leetcode.com/problems/maximum-subarray/) |Medium| [Java](./code/lc53.java)
-
+| 054  |
 | 055  | [Jump Game](https://leetcode.com/problems/jump-game/)  |Medium| [Java](./code/lc55.java)
 | 056  | [Merge Intervals](https://leetcode.com/problems/merge-intervals/) |Medium| [Java](./code/lc56.java)
 | 062  | [Unique Paths](https://leetcode.com/problems/unique-paths/)  |Medium| [Java](./code/lc62.java)

code/lc36.java

+package code;
+/*
+ * 36. Valid Sudoku
+ * 题意：横排，竖排，3*3不能包含相同数字
+ * 难度：Medium
+ * 分类：Hash Table
+ * 思路：用一个Set即可，把行号，列号拼上去
+ * Tips：注意add如果已经有了，返回的是false
+ */
+import java.util.HashSet;
+
+public class lc36 {
+    public boolean isValidSudoku(char[][] board) {
+        HashSet<String> hs = new HashSet();  // 如果此set已包含该元素，则该调用不更改set并返回false。
+        for (int i = 0; i < board.length ; i++) {
+            for (int j = 0; j < board[0].length ; j++) {
+                if(board[i][j]=='.') continue;
+                boolean flag1 = hs.add(board[i][j]+"row"+i);
+                boolean flag2 = hs.add(board[i][j]+"col"+j);
+                boolean flag3 = hs.add(board[i][j]+"box"+i/3+j/3);
+                if((!flag1)||(!flag2)||(!flag3)) {
+                    return false;
+                }
+            }
+        }
+        return true;
+    }
+}

code/lc50.java

+package code;
+/*
+ * 50. Pow(x, n)
+ * 题意：幂运算
+ * 难度：Medium
+ * 分类：Math, Binary Search
+ * 思路：和lc29的思路类似，数值上的二分。用前一步的结果进行下一步的运算，降低了迭代次数
+ * Tips：注意溢出的情况，负数的情况。
+ */
+public class lc50 {
+    public double myPow(double x, int n) {
+        if(n == 0) return 1;
+        if(n==Integer.MIN_VALUE && x!=1 && x!=-1) return 0;
+        if(n<0){
+            n = -n;
+            x = 1/x;    //负数变成 1/x
+        }
+        return (n%2 == 0) ? myPow(x*x, n/2) : x*myPow(x*x, n/2);
+    }
+}

code/lc54.java

+package code;
+/*
+ * 54. Spiral Matrix
+ * 题意：螺旋输出矩阵
+ * 难度：Medium
+ * 分类：Array
+ * 思路：很直接的思路，就是循环打印
+ * Tips：需要注意很多细节，最后调试成功
+ */
+import java.util.ArrayList;
+import java.util.List;
+
+public class lc54 {
+    public static void main(String[] args) {
+        int[][] matrix = {{1,2,3,4},{5,6,7,8},{9,10,11,12}};
+        System.out.println(spiralOrder(matrix));
+    }
+    public static List<Integer> spiralOrder(int[][] matrix) {
+        List<Integer> res = new ArrayList<>();
+        if(matrix.length==0) return res;
+        int r=0, c=-1;  // -1开始，循环内首先++
+        int row_r = matrix.length;
+        int col_r = matrix[0].length;
+        int row_l = -1;
+        int col_l =-1;
+        while( row_l+1<row_r || col_l+1<col_r ){
+            c++;
+            if(c<col_r){
+                while(c<col_r){
+                    res.add(matrix[r][c]);
+                    c++;
+                }
+            }else   //提前终止
+                return res;
+            c--;    // -- 恢复正常
+            r++;
+            if(r<row_r) {
+                while (r < row_r) {
+                    res.add(matrix[r][c]);
+                    r++;
+                }
+            }else
+                return res;
+            r--;
+            c--;
+            if(c>col_l){
+                while(c>col_l){
+                    res.add(matrix[r][c]);
+                    c--;
+                }
+            }else
+                return res;
+            c++;
+            r--;
+            if(r>row_l+1) {
+                while (r > row_l + 1) {
+                    res.add(matrix[r][c]);
+                    r--;
+                }
+            }else
+                return res;
+            r++;
+            row_l++;
+            row_r--;
+            col_l++;
+            col_r--;
+        }
+        return res;
+    }
+}

readme.md

@@ -39,6 +39,7 @@ Language: Java
 | 032 [Java](./code/lc32.java)
 | 033 [Java](./code/lc33.java)
 | 034 [Java](./code/lc34.java)
+| 036 [Java](./code/lc36.java)
 | 038 [Java](./code/lc38.java)
 | 039 [Java](./code/lc39.java)
 | 041 [Java](./code/lc41.java)
@@ -47,7 +48,9 @@ Language: Java
 | 046 [Java](./code/lc46.java)
 | 048 [Java](./code/lc48.java)
 | 049 [Java](./code/lc49.java)
+| 050 [Java](./code/lc50.java)
 | 053 [Java](./code/lc53.java)
+| 054 [Java](./code/lc54.java)
 | 055 [Java](./code/lc55.java)
 | 056 [Java](./code/lc56.java)
 | 058 [Java](./code/lc58.java)