原题地址：https://oj.leetcode.com/problems/search-a-2d-matrix/
题意：
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.
解题思路：类似于二分查找。
代码：
class Solution:
# @param matrix, a list of lists of integers
# @param target, an integer
# @return a boolean
def searchMatrix(self, matrix, target):
i = 0; j = len(matrix[0]) - 1
while i < len(matrix) and j >= 0:
if matrix[i][j] == target: return True
elif matrix[i][j] > target: j -= 1
else: i += 1
return False