Write an efficient algorithm that searches for a value in an m x n matrix. This matrix has the following properties:

?

• Integers in each row are sorted in ascending from left to right.
• Integers in each column are sorted in ascending from top to bottom.

  ?

  For example,

  Consider the following matrix:

  [
    [1,   4,  7, 11, 15],
    [2,   5,  8, 12, 19],
    [3,   6,  9, 16, 22],
    [10, 13, 14, 17, 24],
    [18, 21, 23, 26, 30]
  ]
  

  Given target = 5, return true.

  Given target = 20, return false.

  实现：
  class Solution {
  public:
  bool searchMatrix(vector >& matrix, int target) {
  int min = 0;
  while (min < matrix.size() && matrix[min][0] <= target) {
  if (searchMatrix(matrix[min], target)) {
  return true;
  }
  min++;
  }
  return false;
  }
  
  bool searchMatrix(vector & matrix, int target) {
  int min = 0;
  int max = matrix.size()-1;
  int mid;
  while (min <= max) {
  mid = (min + max) / 2;
  if (matrix[mid] > target) {
  max = mid-1;
  } else if (matrix[mid] < target) {
  min = mid+1;
  } else {
  return true;
  }
  }
  return false;
  }
  };

  ?