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前言

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一、力扣738. 单调递增的数字

class Solution {public int monotoneIncreasingDigits(int n) {String s = String.valueOf(n);char[] ch = s.toCharArray();int start = s.length();for(int i= ch.length-2; i >= 0; i --){if(ch[i] > ch[i+1]){ch[i] --;start = i+1;}}for(int i = start; i < s.length(); i ++){ch[i] = '9';}return Integer.parseInt(String.valueOf(ch));}
}

二、力扣968. 监控二叉树

/*** Definition for a binary tree node.* public 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;*     }* }*/
class Solution {int res = 0;public int minCameraCover(TreeNode root) {if(fun(root) == 0){res ++;}return res;}/***0表示当前节点未被覆盖*1表示当前节点安装摄像头*2表示当前节点已覆盖*/public int fun(TreeNode root){if(root == null){return 2;}int left = fun(root.left);int right = fun(root.right);if(left == 2 &&  right == 2){return 0;}if(left == 0 || right == 0){res ++;return 1;}if(left == 1 || right == 1){return 2;}return 0;}
}