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5.leetcode/src/com/fanxb/common/Q783.java

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+package com.fanxb.common;
+
+import java.util.Arrays;
+
+/**
+ * Created with IntelliJ IDEA
+ * x 的平方根
+ * 地址： https://leetcode-cn.com/problems/sqrtx/
+ * 思路： 题目要求求解一个数的平方根的整数部分，那就那就相当于找到一个数num,使其满足num*mum==x || num*num<x && (num+1)*(num+1)>x
+ * 可通过二分查找来进行求解，num的值一定是[0,x]中的一个数
+ * 1. 首先设定l=0,r=x
+ * 2. mid=(l+r)/2,temp1=mid*mid,temp2=(mid+1)*(mid+1)
+ * 3. 如果temp1 == x || (temp1 < x && temp2 > x)满足结果即为mid
+ * 4. 否则判断temp1>x,如果满足r=mid,重复2
+ * 5. 否则l=mid,重复2
+ *
+ * @author fanxb
+ * Date: 2020/6/11 9:56
+ */
+public class Q783 {
+    public static class TreeNode {
+        int val;
+        TreeNode left;
+        TreeNode right;
+
+        TreeNode() {
+        }
+
+        TreeNode(int val) {
+            this.val = val;
+        }
+
+        TreeNode(int val, TreeNode left, TreeNode right) {
+            this.val = val;
+            this.left = left;
+            this.right = right;
+        }
+    }
+
+    public int minDiffInBST(TreeNode root) {
+        int min = Integer.MAX_VALUE;
+        //找到左边的最大值和右边的最小值即可
+        if (root.left != null) {
+            TreeNode maxLeft = root.left;
+            while (maxLeft.right != null) {
+                maxLeft = maxLeft.right;
+            }
+            min = root.val - maxLeft.val;
+            min = Math.min(min, minDiffInBST(root.left));
+        }
+        if (root.right != null) {
+            TreeNode minRight = root.right;
+            while (minRight.left != null) {
+                minRight = minRight.left;
+            }
+            min = Math.min(min, minRight.val - root.val);
+            min = Math.min(min, minDiffInBST(root.right));
+        }
+        return min;
+    }
+
+    public static void main(String[] args) {
+        TreeNode root = new TreeNode(90);
+        root.left = new TreeNode(69);
+        root.left.left = new TreeNode(49);
+        root.left.right = new TreeNode(89);
+        root.left.left.right = new TreeNode(52);
+        System.out.println(new Q783().minDiffInBST(root));
+    }
+}