set matrix zero@leetcode

刷题必备书籍：Cracking the Coding Interview: 150 Programming Questions and Solutions 

简历：The Google Resume: How to Prepare for a Career and Land a Job at Apple, Microsoft, Google, or any Top Tech Company
算法学习书籍：Introduction to Algorithms
编程珠玑：Programming Pearls (2nd Edition)
C++ 学习：The C++ Programming Language, 4th Edition
经典操作系统书籍，龙书：Operating System Concepts
创业：The Start-up of You: Adapt to the Future, Invest in Yourself, and Transform Your Career

Given a m x n matrix, if an element is 0, set its entire row and column to 0. Do it in place.

click to show follow up.

Follow up:

Did you use extra space?
A straight forward solution using O(mn) space is probably a bad idea.
A simple improvement uses O(m + n) space, but still not the best solution.
Could you devise a constant space solution?

这道题不难，不能用additional space，那么用第一行和第一列作为标记的地方。

但是要注意几点：

1. 用bool变量来标记第一行第一列需要不需要set zero，并且最后再做。

2. 在标记完set zero时，不要先动第一行和第一列，不然假如matrix[0][0]==0,那么第一列全set 为 0， 之后的信息就丢失了，所以从1开始set。