[Leetcode] 111. Minimum Depth of Binary Tree

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.

这个题要注意叶子节点的定义。某个子树是null的时候，它不是叶子节点。这个时候就算没形成一个叶子到root的path，则depth为正无穷。

public class Solution {
    public int minDepth(TreeNode root) {
        if(root==null) return 0;
        if(root.left==null) return minDepth(root.right)+1;
        if(root.right==null) return minDepth(root.left)+1;
        return Math.min(minDepth(root.left)+1,minDepth(root.right)+1);
    }
}