二叉树篇

中序遍历实现

/*** 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 {private long pre=Long.MIN_VALUE;public boolean isValidBST(TreeNode root) {if(root==null){return true;}if(!isValidBST(root.left)||root.val<=pre){return false;}pre=root.val;return isValidBST(root.right);}
}