【C++】LeetCode 85. Maximal Rectangle

题目：

Given a 2D binary matrix filled with 0's and 1's, find the largest rectangle containing only 1's and return its area.

For example, given the following matrix:

1 0 1 0 01 0 1 1 11 1 1 1 11 0 0 1 0

Return 6.

思路：

这一题参考84题（http://blog.csdn.net/lv1224/article/details/72461540）的思路。矩形每一列可以看做一个柱状图。

用动态规划，每一行调用84题程序，即可求解。

代码：

/*参考84题 LeetCode 84. Largest Rectangle in Histogram*/class Solution {public:    int largestRectangleArea(vector<int>& heights) {        stack<int> index;        int maxarea=0;        int i=0;        while(!index.empty()||i<heights.size())        {            if(index.empty()||(i<heights.size()&&heights[i]>heights[index.top()]))            {                index.push(i++);            }            else            {                int temp=heights[index.top()];                index.pop();                maxarea=max(maxarea,temp*(i-(index.empty()?0:index.top()+1)));            }        }        return maxarea;    }    int maximalRectangle(vector<vector<char>>& matrix) {        if(matrix.size()==0||matrix[0].size()==0)return 0;        vector<int> heights(matrix[0].size(),0);        int res=0;        for(int i=0;i<matrix.size();i++)        {            for(int j=0;j<matrix[0].size();j++)            {                if(matrix[i][j]=='0')heights[j]=0;                else heights[j]+=1;            }            res=max(res,largestRectangleArea(heights));        }        return res;    }};