力扣算法题—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.

Note: A leaf is a node with no children.

Example:

Given binary tree [3,9,20,null,null,15,7],

    3
   /   9  20
    /     15   7

return its minimum depth = 2.

Solution:

　　使用深度遍历和广度遍历

 1 class Solution {
 2 private:
 3     int minLevel = INT32_MAX;
 4 public:
 5     int minDepth(TreeNode* root) {
 6         if (root == nullptr)return 0;
 7         //return BFS(root);
 8         int res = INT32_MAX;
 9         DFS(root, 1, res);
10         return res;
11     }
12
13     int BFS(TreeNode* root)
14     {
15         queue<TreeNode*>q;
16         q.push(root);
17         int level = 0;
18         while (!q.empty())
19         {
20             queue<TreeNode*>temp;
21             ++level;
22             while (!q.empty())
23             {
24                 TreeNode* p = q.front();
25                 q.pop();
26                 if (p->left == nullptr && p->right == nullptr)return level;
27                 if (p->left != nullptr)temp.push(p->left);
28                 if (p->right != nullptr)temp.push(p->right);
29             }
30             q = temp;
31         }
32         return level;
33     }
34     void DFS(TreeNode* root, int level, int &res)
35     {
36         if (root->left == nullptr && root->right == nullptr) {
37             res = res > level ? level : res;
38             return;
39         }
40         if (root->left != nullptr)DFS(root->left, level + 1, res);
41         if (root->right != nullptr)DFS(root->right, level + 1, res);
42     }
43
44 };

原文地址：https://www.cnblogs.com/zzw1024/p/11756228.html