LeetCode My Solution: Minimum Depth of Binary Tree

Minimum Depth of Binary Tree

 Total Accepted: 24760 Total Submissions: 83665My Submissions

Given a binary tree, find its minimum depth.

The minimum depth is the number of nodes along the shortest path from the root node down to the nearest leaf node.

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/**
 * Definition for binary tree
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public int minDepth(TreeNode root) {
        if (root == null){
            return 0;
        }
      return helper(root);
    }
    //这个题目和求最大(最小深度)不一样的是要走到叶子节点才算行,也就说要到了叶子节点才OK
    //最開始的时候採取了(root == null)的推断，报错，是由于对根节点的处理中觉得是求最大的深度。而最小的深度实际是到了
    //叶子节点之后才算行
    int helper(TreeNode root) {
        if (root.left == null && root.right == null) {
            return 1;
        }
        if (root.left == null) {
            return helper(root.right) + 1;
        }     
        if (root.right == null) {
            return helper(root.left) + 1;
        }
        else {
        return Math.min(helper(root.left),helper(root.right)) + 1;
        }
    }
}