【hot100-java】【对称二叉树】

R8-二叉树篇

思路：

DFS搜索+递归分解成子问题逐步判断即可。

/**
 * 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 {
    public boolean isSymmetric(TreeNode root) {
        return root==null || recur(root.left,root.right);
    }
    boolean recur(TreeNode L,TreeNode R){
        if (L==null && R==null) return true;
        if (L==null || R==null || L.val!=R.val) return false;
        return recur(L.left,R.right)&&recur(L.right,R.left);
    }
}

真-没落的java