leetcode240 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.
"""
"""
剑指offer原题，很经典的一道题
AC
"""
class Solution:
    def searchMatrix(self, matrix, target):
        """
        :type matrix: List[List[int]]
        :type target: int
        :rtype: bool
        """
        if not matrix:
            return False
        m = len(matrix)
        n = len(matrix[0])
        i, j = m-1, 0
        while i >= 0 and j < n:
            if target > matrix[i][j]:
                j += 1
            elif target < matrix[i][j]:
                i -= 1
            else:
                return True
        return False