[Leetcode] 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.

 

Solution:

第一次提交的错误的代码。

比如a#b这种左子树为空的树，我直接认为左子树的depth为0了，那当然左子树的depth小，然后parent直接取了0+1。问题在于，某个子树是null的时候，它不是叶子节点啊！这个时候就算没形成一个叶子到root的path，则认为depth为正无穷。

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

 

 

修改过后正确的代码是：

/**
 * 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;
        if(root.left==null&&root.right==null)
            return 1;
        int lDepth=minDepth(root.left);
        int rDepth=minDepth(root.right);
        if(root.left==null){
            lDepth=Integer.MAX_VALUE;
        }
        if(root.right==null){
            rDepth=Integer.MAX_VALUE;
        }
        return Math.min(rDepth,lDepth )+1;
    }
}