Search a 2D Matrix

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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.

经典的二分查找的题目。

这题有个特点是每一行有序，且每一行开头数字大于上一行最后的数字，即如果按行flatten,可以拉伸成为一个有序数组。

思路： 1.先在垂直方向二分，找出行，再在行上二分找出列。复杂度O(logm+logn)2.把数组拉成一维处理(坐标处理为连续的一维),时间复杂度为O(logm*n)==O(logm+logn).

思路有了，代码简单，就不贴了。

Search a 2D Matrix

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原文地址：http://www.cnblogs.com/sherylwang/p/5786996.html