動機

複習saddle back

Problem

Write an efficient algorithm that searches for a target value in an m x n integer matrix. The 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 1:

Input: 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]], target = 5Output: true

Example 2:

Input: 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]], target = 20Output: false

 

Constraints:

  • m == matrix.length
  • n == matrix[i].length
  • 1 <= n, m <= 300
  • -109 <= matix[i][j] <= 109
  • All the integers in each row are sorted in ascending order.
  • All the integers in each column are sorted in ascending order.
  • -109 <= target <= 109

Sol

詳細去看saddleback-search-algorithm

class Solution:
    def searchMatrix(self, ms: List[List[int]], val: int) -> bool:
        a,b = len(ms)-1,0
        while 0 <= a < len(ms) and 0 <= b < len(ms[a]):
            if ms[a][b] == val:
                return True
            elif ms[a][b] < val:
                b += 1
            else:
                a -= 1
        return False