Q:

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.

Analysis:

此題要求返回二叉樹根結點到葉子結點最短的距離。

可以採用遞迴的方法：

Code:

/**
 * 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) {
            return minDepth(root.right) + 1;
        }
        if
 
 (root.right == null) {
            return minDepth(root.left) + 1;
        }
        return Math.min(minDepth(root.left), minDepth(root.right)) + 1;
    }
}