力扣668.乘法表中第k小的数

力扣668.乘法表中第k小的数

• 二分查找

  • 是否有k个比mid小的数

  class Solution {
  public:
      int findKthNumber(int m, int n, int k) {
          auto check = [&](int mid) -> bool
          {
              int res=0;
              int row = 1,col = n;
              while(row <= m)
              {
                  if(row * col <= mid)
                  {
                      res += col;
                      if(res >= k) return false;
                      row ++;
                  }
                  else col --;
              }
              return true;
          };
          int l = 1,r = n * m;
          while(l<r)
          {
              int mid = l + r + 1 >> 1;
              if(check(mid)) l = mid;
              else r = mid - 1;
          }
          return r + 1;
      }
  };