LeetCode 111. 二叉树的最小深度

示例:

给定二叉树 [3,9,20,null,null,15,7],

    3
   / \
  9  20
    /  \
   15   7
返回它的最小深度  2.

class Solution {
public:
    int minDepth(TreeNode* root) {
        if(root == NULL)
            return 0;
        int leftHeight, rightHeight;
        if(root->left && root->right)
        {
            leftHeight = minDepth(root->left);
            rightHeight = minDepth(root->right);
        }
        else if(root->left && !root->right)
        {
            leftHeight = minDepth(root->left);
            rightHeight = INT_MAX;
        }
        else if(!root->left && root->right)
        {
            leftHeight = INT_MAX;
            rightHeight = minDepth(root->right);
        }
        else
        {
            leftHeight = rightHeight = 0;
        }
        return min(leftHeight, rightHeight)+1;
    }
};

class Solution {//BFS
public:
    int minDepth(TreeNode* root) {
        if(root == NULL)
            return 0;
        int height = 0, n;
        queue<TreeNode*> q;
        q.push(root);
        while(!q.empty())
        {
            height++;
            n = q.size();
            while(n--)
            {
                if(!q.front()->left && !q.front()->right)//第一个叶子节点退出
                    return height;
                if(q.front()->left)
                    q.push(q.front()->left);
                if(q.front()->right)
                    q.push(q.front()->right);
                q.pop();
            }
        }
        return height;
    }
};