240. Search a 2D Matrix II

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.

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.

解题要点：

如果当前数字小于目标数字，往右找；如果大于目标数字，往上找。

class Solution(object):
    def searchMatrix(self, matrix, target):
        """
        :type matrix: List[List[int]]
        :type target: int
        :rtype: bool
        """
        n = len(matrix)
        if n == 0:
            return False
        m = len(matrix[0])
        i = n - 1
        j = 0
        if m == 0:
            return False
        while i >= 0 and j < m:
            if matrix[i][j] < target:
                j += 1
            elif matrix[i][j] > target:
                i -= 1
            else:
                return True
        return False