刷题牛客

class Solution {
public:
  /**
   *
   * @param root TreeNode类
   * @return int整型vector<vector<>>
   */
  vector<vector<int> > levelOrder(TreeNode* root) {
      // write code here
      queue<TreeNode*> q;
      vector<vector<int>> res;
      if(!root) return res; // 这个也会发生段错误
      else q.push(root);
      while (q.size() > 0) {
          int s = q.size();
          vector<int> temp;
          for (int i = 0; i < s; i++) {
              temp.push_back(q.front()->val);
              if (q.front()->left != NULL) q.push(q.front()->left);
              if (q.front()->right != NULL) q.push(q.front()->right);
              q.pop();
          }
          res.push_back(temp);
      }
      return res;
  }
};

class Solution {
public:
  /**
   * 二分查找
   * @param n int整型 数组长度
   * @param v int整型 查找值
   * @param a int整型vector 有序数组
   * @return int整型
   */
  int upper_bound_(int n, int v, vector<int>& a) {
      // write code here
      int left = 0, right = a.size() - 1;
      while (left < right) {
          int mid = left + right >> 1;
          if(a[mid] >= v) {
              right = mid;
          } else {
              left = mid+1;
          }
      }
      if(a[right] >= v) return right + 1;
      else return right + 2;
  }
};