LeetCode – Refresh – Minimum Depth of Binary Tree

/**
 * 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) {
        if (!root) return 0;
        queue<TreeNode *> q;
        q.push(root);
        int current = 1, future = 0, level = 1;
        while (!q.empty()) {
            TreeNode *tmp = q.front();
            q.pop(), current--;
            if (!tmp->left && !tmp->right) return level;
            if (tmp->left) {
                q.push(tmp->left);
                future++;
            }
            if (tmp->right) {
                q.push(tmp->right);
                future++;
            }
            if (!current) {
                current = future;
                future = 0;
                level++;
            }
        }
    }
};