LeetCode刷题笔记（树）：minimum-depth-of-binary-tree

「爱情、让人受尽委屈。」 2022-05-31 04:29 178阅读 0赞

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*  **转载请注明作者和出处：[http://blog.csdn.net/u011475210][http_blog.csdn.net_u011475210]**
 *  **代码地址：[https://github.com/WordZzzz/Note/tree/master/LeetCode][https_github.com_WordZzzz_Note_tree_master_LeetCode]**
 *  **刷题平台：[https://www.nowcoder.com/ta/leetcode][https_www.nowcoder.com_ta_leetcode]**
 *  **题  库：Leetcode经典编程题**
 *  **编  者：WordZzzz**

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*   *  题目描述
     *  解题思路
     *  C版代码实现
        
         *  深度优先搜索
         *  广度优先搜索

## 题目描述 ##

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.

给定一棵二叉树，找到它的最小深度。最小深度是沿着从根节点到最近叶节点的最短路径的节点数量。

## 解题思路 ##

DFS和BFS都可以，但是很明显，BFS更快，因为BFS只要找到第一个叶子结点就可以停止遍历了看，而DFS需要通过迭代来遍历所有的结点。

这里我重点说一下BFS，循环的终止条件是now结点无左右子树，即size前后无变化。

## C++版代码实现 ##

### 深度优先搜索 ###

class Solution {
    public:
        int run(TreeNode *root) {
            if(root == NULL)
                return false;
            if(root->left == NULL)
                return run(root->right) + 1;
            if(root->right == NULL)
                return run(root->left) + 1;
            int leftDepth = run(root->left);
            int rightDepth = run(root->right);
            return min(leftDepth, rightDepth) + 1;
        }
    };

### 广度优先搜索 ###

class Solution {
    public:
        int run(TreeNode *root) {
            if(root == NULL)
                return false;
            queue<TreeNode *> que;
            TreeNode *last, *now;
            int level = 1, size = 0;
            last = now = root;
            que.push(root);
            while(!que.empty()){
                now = que.front();
                que.pop();
                size = que.size();
                if(now->left)
                    que.push(now->left);
                if(now->right)
                    que.push(now->right);
                if(que.size() == size)  //循环终止条件
                    break;
                if(last == now){
                    level++;
                    if(que.size() != 0)
                        last = que.back();
                }
            }
            return level;
        }
    };

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[http_blog.csdn.net_u011475210]: http://blog.csdn.net/u011475210
[https_github.com_WordZzzz_Note_tree_master_LeetCode]: https://github.com/WordZzzz/Note/tree/master/LeetCode
[https_www.nowcoder.com_ta_leetcode]: https://www.nowcoder.com/ta/leetcode