代码随想录：找树左下角的值

层次遍历轻轻松松

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left),
 * right(right) {}
 * };
 */
class Solution {
public:
    int findBottomLeftValue(TreeNode* root) {
        if (!root)
            return 0;
        queue<TreeNode*> que;
        que.push(root);
        while (!que.empty()) {
            int this_left;
            int next_size = 0;
            int size = que.size();
            for (int i = 0; i < size; i++) {
                TreeNode* target = que.front();
                que.pop();
                if (i == 0)
                    this_left = target->val;
                if (target->left) {
                    que.push(target->left);
                    next_size++;
                }
                if (target->right) {
                    que.push(target->right);
                    next_size++;
                }
            }
            if (next_size == 0)
                return this_left;
        }
        return 0;
    }
};