LN : leetcode 513 Find Bottom Left Tree Value

lc 513 Find Bottom Left Tree Value

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513 Find Bottom Left Tree Value

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.

BFS Accepted##

这个问题如果按照惯性思维从左到右进行BFS会陷入僵局，但是如果从右往左做BFS就特别简单，最下层的最左值即为最后一次从队列中出来的节点的值。

/**
 * 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);
        auto temp = root;
        while (!q.empty()) {
            temp = q.front();
            q.pop();
            if (temp->right) q.push(temp->right);
            if (temp->left) q.push(temp->left);
        }
        return temp->val;
    }
};