daily question---20/8/9

java-leetcode/src/main/java/io/github/wkk/everyday/aug/RecoverBinarySearchTree.java

+/* All Contributors (C) 2020 */
+package io.github.wkk.everyday.aug;
+
+import io.github.wkk.structs.TreeNode;
+import java.util.ArrayDeque;
+import java.util.Deque;
+
+/**
+ * 恢复二叉搜索树
+ *
+ * <p>难点: 找出真正出问题的两个点
+ *
+ * <p>思路: 根据其性质, 使用中序遍历, 标记出真正出现问题的两个位置, 之后交换其元素值即可
+ *
+ * <p>抽象: .....errorOne |increasing sequence | errorTwo .......
+ *
+ * <p>第一个节点,是第一个按照中序遍历时候前一个节点大于后一个节点,我们选取前一个节点
+ *
+ * <p>第二个节点,是在第一个节点找到之后, 后面出现前一个节点大于后一个节点,我们选择后一个节点
+ *
+ * @author kongwiki@163.com
+ * @since 2020/8/8上午8:59
+ */
+public class RecoverBinarySearchTree {
+    private TreeNode errorOne, errorTwo;
+
+    public void recoverTree(TreeNode root) {
+        helper(root);
+        swap(errorOne, errorTwo);
+    }
+
+    private void helper(TreeNode root) {
+        if (root == null) {
+            return;
+        }
+        TreeNode pre = null;
+        Deque<TreeNode> stack = new ArrayDeque<>();
+        TreeNode p = root;
+        while (!stack.isEmpty() || p != null) {
+            if (p != null) {
+                stack.push(p);
+                p = p.left;
+            } else {
+                p = stack.pop();
+                if (pre != null && pre.val > p.val) {
+                    if (errorOne == null) {
+                        errorOne = pre;
+                        errorTwo = p;
+                    } else {
+                        errorTwo = p;
+                    }
+                }
+                pre = p;
+                p = p.right;
+            }
+        }
+    }
+
+    private void swap(TreeNode first, TreeNode second) {
+        int temp = first.val;
+        first.val = second.val;
+        second.val = temp;
+    }
+}

java-leetcode/src/main/java/io/github/wkk/everyday/aug/RestoreIPAddresses.java

+/* All Contributors (C) 2020 */
+package io.github.wkk.everyday.aug;
+
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * 复原IP地址(IP格式: 每一位都在0-255之间)
+ *
+ * <p>思路: 1.暴力求解 2.回溯(涉及到求所有的结果, 常用方法)
+ *
+ * @author kongwiki@163.com
+ * @since 2020/8/9上午9:33
+ */
+public class RestoreIPAddresses {
+    /** 暴力求解 需要一个辅助方法, 判断每个子串是否符合IP格式 1. 每位在0-255之间 2. 不能出现0开头的两位以上数字 */
+    public List<String> restoreIpAddresses(String s) {
+        List<String> res = new ArrayList<>();
+        if (s == null || s.length() == 0 || s.length() > 12) {
+            return res;
+        }
+        int n = s.length();
+        for (int i = 0; i < 3; i++) {
+            for (int j = i + 1; j < i + 4; j++) {
+                for (int k = j + 1; k < j + 4; k++) {
+                    if (j < n && k < n) {
+                        String a = s.substring(0, i + 1);
+                        String b = s.substring(i + 1, j + 1);
+                        String c = s.substring(j + 1, k + 1);
+                        String d = s.substring(k + 1);
+                        if (helper(a) && helper(b) && helper(c) && helper(d)) {
+                            StringBuilder sb = new StringBuilder();
+                            sb.append(a)
+                                    .append(".")
+                                    .append(b)
+                                    .append(".")
+                                    .append(c)
+                                    .append(".")
+                                    .append(d);
+                            res.add(sb.toString());
+                        }
+                    }
+                }
+            }
+        }
+        return res;
+    }
+
+    private boolean helper(String s) {
+        if (s == null
+                || s.length() == 0
+                || s.length() > 3
+                || s.charAt(0) == '0' && s.length() > 1
+                || Integer.parseInt(s) > 255) {
+            return false;
+        }
+        return true;
+    }
+
+    /** 回溯 */
+    public List<String> restoreIpAddressesII(String s) {
+        List<String> res = new ArrayList<>();
+        if (s == null || s.length() == 0 || s.length() > 12) {
+            return res;
+        }
+        int n = s.length();
+        backtrack(0, "", 4, s, n, res);
+        return res;
+    }
+
+    /** 回溯本体 */
+    private void backtrack(int start, String tmp, int flag, String s, int n, List<String> res) {
+        if (start == n && flag == 0) {
+            res.add(tmp.substring(0, tmp.length() - 1));
+            return;
+        }
+        if (flag < 0) {
+            return;
+        }
+        for (int j = start; j < start + 3; j++) {
+            if (j < n) {
+                if (start == j && s.charAt(j) == '0') {
+                    backtrack(j + 1, tmp + s.charAt(j) + ".", flag - 1, s, n, res);
+                    break;
+                }
+                if (Integer.parseInt(s.substring(start, j + 1)) <= 255) {
+                    backtrack(j + 1, tmp + s.substring(start, j + 1) + ".", flag - 1, s, n, res);
+                }
+            }
+        }
+    }
+}

java-leetcode/src/main/java/io/github/wkk/everyday/aug/SameTree.java

+/* All Contributors (C) 2020 */
+package io.github.wkk.everyday.aug;
+
+import io.github.wkk.structs.TreeNode;
+
+/**
+ * @author kongwiki@163.com
+ * @since 2020/8/7上午8:58
+ */
+public class SameTree {
+    public boolean isSameTree(TreeNode p, TreeNode q) {
+        if (p == null && q == null) {
+            return true;
+        } else if (p == null || q == null) {
+            return false;
+        } else if (p.val != q.val) {
+            return false;
+        } else {
+            return isSameTree(p.left, q.left) && isSameTree(p.right, q.right);
+        }
+    }
+}

java-leetcode/src/main/java/io/github/wkk/wkk.md

@@ -9,7 +9,9 @@
 4. [207. 课程表](./everyday/aug/CourseSchedule.java)
 5. [337. 打家劫舍III](./everyday/aug/HouseRobberIII.java)
 6. [336. 回文对](./everyday/aug/PalindromePairs.java)
-
+7. [100. 相同的树](./everyday/aug/SameTree.java)
+8. [99. 恢复二叉搜索树](./everyday/aug/RecoverBinarySearchTree.java)
+9. [93. 复原IP地址](./everyday/aug/RestoreIPAddresses.java)
 ## 哈希表
 1. [1. 两数之和](./TwoSum.java)