Maximal Rectangle

题目大意：一个矩阵，每个格子为0或1，求这个矩阵的最大子矩阵，这个子矩阵里面每个格子都为1.

解题思路：单调栈。

遍历每行，可以求出该列的包含1的高度，转换成“Largest Rectangle in Histogram” 问题。http://blog.csdn.net/xiaoxiaoluo/article/details/43883081

class Solution {public:    int maximalRectangle(vector<vector<char> > &matrix) {          if(matrix.empty() || matrix[0].empty())          return 0;        int m = matrix.size();        int n = matrix[0].size();        vector<int> height(n, 0);        vector<int> stack;        int area = 0, index, width;        for(int i = 0; i < m; i++) {            stack.clear();            for(int j = 0; j < n; j++) {                if(matrix[i][j] == '0') {                    height[j] = 0;                } else {                    height[j] += 1;                }                while(!stack.empty() && height[stack.back()] > height[j]) {                    index = stack.back();                    stack.pop_back();                    width = stack.empty() ? j : j  - 1 - stack.back();                    area = max(area, height[index] * width);                }                stack.push_back(j);            }             while(!stack.empty()) {                index = stack.back();                stack.pop_back();                width = stack.empty() ? n : n - 1 - stack.back();                area = max(area, height[index] * width);            }        }        return area;    }};