leetcode No240. Search a 2D Matrix II

Posted 2022-06-11 Dufre.WC

Question

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.

Algorithm

start from top-right -> bottom-left, or start from bottom-left -> top-right

Accepted Code

class Solution:
    def searchMatrix(self, matrix, target):
        """
        :type matrix: List[List[int]]
        :type target: int
        :rtype: bool
        """
        if not matrix or not matrix[0]:
            return False
        
        row, column = len(matrix), len(matrix[0])
        i, j = 0, column-1
        while i<row and j>=0:
            if target == matrix[i][j]:
                return True
            if target < matrix[i][j]:
                j-=1
            else:
                i+=1
        return False