111. Minimum Depth of Binary Tree - jiejackyzhang/leetcode-note GitHub Wiki

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.

Tree类题目。

解题思路为recursion。 注意点是几个basic cases：

1. root == null;
2. root.left == null && root.right == null;
3. root.left和root.right只有一个为null;
4. root.left和root.right都不为null.

/**
 * Definition for a binary tree node.
 * 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;
        if(root.left == null && root.right == null) return 1;
        if(root.left == null || root.right == null) return Math.max(minDepth(root.left), minDepth(root.right)) + 1;
        return Math.min(minDepth(root.left), minDepth(root.right)) + 1;
    }
}