image.png

思路：

  • 依然是标准的层次遍历二叉树
  • 采用了for循环，i == 0 的时候，必然就是最左边的数值，而最后一次更新的“最左边的数值”，就是最底层的最左边的数值

代码：

  1. /**
  2.  * Definition for a binary tree node.
  3.  * struct TreeNode {
  4.  *     int val;
  5.  *     TreeNode *left;
  6.  *     TreeNode *right;
  7.  *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
  8.  *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
  9.  *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
  10.  * };
  11.  */
  12. class Solution {
  13. public:
  14.     int findBottomLeftValue(TreeNode* root) {
  15.         int bottom_left = 0;
  16.         queue<TreeNode*> q;
  17.         q.push(root);
  19.         while (!q.empty()) {
  20.             int cur_level_size = q.size();
  21.             for (int i = 0; i < cur_level_size; ++i) {
  22.                 TreeNode* node = q.front();
  23.                 q.pop();
  24.                 if (i == 0) {
  25.                     bottom_left = node->val;
  26.                 }
  28.                 if (node->left) q.push(node->left);
  29.                 if (node->right) q.push(node->right);
  30.             }
  31.         }
  33.         return bottom_left;
  34.     }
  35. };