【leetcode】Minimum Depth of Binary Tree

Question ： 

 

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.

 

Anwser 1 ：   

 

/**

 * Definition for binary tree

 * struct TreeNode {

 *     int val;

 *     TreeNode *left;

 *     TreeNode *right;

 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}

 * };

 */

class Solution {

public:

    int minDepth(TreeNode *root) {

        // Start typing your C/C++ solution below

        // DO NOT write int main() function

        if (root == NULL) return 0;

        

        int left = minDepth(root->left) + 1;

        int right = minDepth(root->right) + 1;

        

        // leaf

        if (left == 1 || right == 1)

            return left > right ? left : right;

            

        return left < right ? left : right;

    }

};

Anwser 2 ：    

 

/**

 * Definition for binary tree

 * struct TreeNode {

 *     int val;

 *     TreeNode *left;

 *     TreeNode *right;

 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}

 * };

 */

class Solution {

public:

    int minDepth(TreeNode *root) {

        // Start typing your C/C++ solution below

        // DO NOT write int main() function

        if (root == NULL) return 0;

        

        int depth = 1;

        queue <TreeNode *> current;

        queue <TreeNode *> next;

        current.push(root);

    

        while (!current.empty())

        {

            while (!current.empty())

            {

                TreeNode *n = current.front();

                current.pop();

                if (n->left==NULL && n->right == NULL) return depth;

                if (n->left) next.push(n->left);

                if (n->right) next.push(n->right);

            }

            

            queue <TreeNode *> t;   // init queue

            current = next;

            next = t;

            depth += 1;

        }

        return depth;

    }

};