[Leetcode]@python 74. Search a 2D Matrix

题目链接

https://leetcode.com/problems/search-a-2d-matrix/

题目原文

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 from left to right.
• The first integer of each row is greater than the last integer of the previous row.

For example,
Consider the following matrix:

[
[1, 3, 5, 7],
[10, 11, 16, 20],
[23, 30, 34, 50]
]

Given target = 3, return true.

题目大意

在m x n的矩阵中，该矩阵满足1）每一行从小到大排列 2）前一行的最后一个元素小于这一行的第一个元素，给定某个数，返回这个数是否存在于矩阵中的布尔值

解题思路

从右上角开始, 比较target 和 matrix[i][j]的值. 如果小于target, 则该行不可能有此数, 所以i++; 如果大于target, 则该列不可能有此数, 所以j--. 遇到边界则表明该矩阵不含target.

代码

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