513. Find Bottom Left Tree Value

题目

Given a binary tree, find the leftmost value in the last row of the tree.

Example 1:
Input:

  2 / \1   3

Output:
1
Example 2:
Input:

    1   / \  2   3 /   / \4   5   6   /  7

Output:
7
Note: You may assume the tree (i.e., the given root node) is not NULL.

题意

找出一棵树最下面一层最左边的数.

分析

使用BFS, 对每一层保留第一个数, 直到结束.

实现

/** * Definition for a binary tree node. * struct TreeNode { *     int val; *     TreeNode *left; *     TreeNode *right; *     TreeNode(int x) : val(x), left(NULL), right(NULL) {} * }; */class Solution {public:    int findBottomLeftValue(TreeNode* root) {        queue<TreeNode*> q;        q.push(root);        int last = root->val;        TreeNode *cur = root;        while (!q.empty()) {            int n = q.size();            last = (q.front())->val;            while (n--) {                cur = q.front();                if (cur->left) q.push(cur->left);                if (cur->right) q.push(cur->right);                q.pop();            }            if(q.empty())                return last;        }    }};