LeetCode:Minimum Depth of Binary Tree

标题叙述性说明：

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.

思路：採用BFS遍历二叉树，在遍历的过程中记录每一个节点的深度，当遇到第一个叶子结点时返回当前叶子结点的深度。

代码：

int Solution::minDepth(TreeNode *root)
{
    int min_height = 0;
    queue<pair<TreeNode *,int> > treeNode_queue;
    if(root == NULL)
        return 0;
    treeNode_queue.push(pair<TreeNode *,int>(root,1));
    while(!treeNode_queue.empty())
    {
        pair<TreeNode *,int> node = treeNode_queue.front();
        treeNode_queue.pop();
        if(node.first->left == NULL && node.first->right == NULL)
        {
            min_height = node.second;
            break;
        }
        if(node.first->right != NULL)
            treeNode_queue.push(pair<TreeNode *,int>(node.first->right,node.second+1));
        if(node.first->left != NULL)
            treeNode_queue.push(pair<TreeNode *,int>(node.first->left,node.second+1));
    }
    return min_height;
}