LC.P1123[最深叶节点的最近公共祖先]

方法一：DFS

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/**
 * 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 {
    
    TreeNode ans;
    int maxDepth = -1;

    public TreeNode lcaDeepestLeaves(TreeNode root) {
        dfs(root, 0);
        return ans;
    }

    private int dfs(TreeNode node, int depth) {
        if (node == null) {
            maxDepth = Math.max(maxDepth, depth);
            return depth;
        }
        int leftMaxDepth = dfs(node.left, depth + 1);
        int rightMaxDepth = dfs(node.right, depth + 1);
        if (leftMaxDepth == rightMaxDepth && leftMaxDepth == maxDepth) {
            ans = node;
        }
        return Math.max(leftMaxDepth, rightMaxDepth); // 返回当前子树的最大深度
    }
}
  • 时间复杂度：$O(n)$
  • 空间复杂度：$O(n)$