Leetcode74搜索二维矩阵

74搜索二维矩阵

编写一个高效的算法来判断 m x n 矩阵中，是否存在一个目标值。该矩阵具有如下特性：

每行中的整数从左到右按升序排列。 每行的第一个整数大于前一行的最后一个整数。 示例 1:

输入:
matrix = [
  [1,   3,  5,  7],
  [10, 11, 16, 20],
  [23, 30, 34, 50]
]
target = 3
输出: true

示例 2:

输入:
matrix = [
  [1,   3,  5,  7],
  [10, 11, 16, 20],
  [23, 30, 34, 50]
]
target = 13
输出: false

来源：力扣（LeetCode） 链接：https://leetcode-cn.com/problems/search-a-2d-matrix 著作权归领扣网络所有。商业转载请联系官方授权，非商业转载请注明出处。

Solution 1

两次二分查找

class Solution:
    def searchMatrix(self, matrix: [[int]], target: int) -> bool:
        if (matrix == [] or matrix == [[]]):
            return False
        start = 0
        end = len(matrix) - 1
        mid = 0
        while (start <= end):
            mid = int((start + end)/2)
            if (target >= matrix[mid][0] and (mid == len(matrix)-1 or target < matrix[mid+1][0])):
                break
            elif (target < matrix[mid][0]):
                end = mid - 1
            else:  # (target > matrix[mid][0])
                start = mid + 1
        line = matrix[mid]
        start = 0
        end = len(line) - 1
        mid = 0
        while (start <= end):
            mid = int((start + end)/2)
            if (target == line[mid]):
                return True
            elif (target < line[mid]):
                end = mid - 1
            else:  # (target > line[mid])
                start = mid + 1
        return False