Maximal Rectangle

https://leetcode.com/problems/maximal-rectangle/

具体算法请参照 largest rectangle in histrogram

code

class Solution {
public:
    int maximalRectangle(vector<vector<char>>& matrix) {
        int m = matrix.size();
        if(m == 0)
        {
            return 0;
        }

        int n = matrix[0].size();
        if(n == 0)
        {
            return 0;
        }

        vector<vector<int>> dp(m, vector<int>(n, 0));

        for(int i = 0; i<m; i++)
        {
            for(int j = 0; j<n; j++)
            {
                if(matrix[i][j] == '1')
                {
                    if(i == 0)
                    {
                        dp[i][j] = 1;
                    }
                    else
                    {
                        dp[i][j] = dp[i-1][j] + 1;
                    }
                }
            }
        }

        int max_area = 0;

        for(int i = 0; i<m; i++)
        {
            dp[i].push_back(-1);
            vector<int> stack;
            for(int j = 0; j<n+1; j++)
            {
                while(!stack.empty() && dp[i][j] <= dp[i][stack.back()])
                {
                    int h = dp[i][stack.back()];
                    stack.pop_back();
                    int w = stack.empty()?j:j-stack.back()-1;
                    max_area = max(max_area, h*w);
                }
                stack.push_back(j);
            }
        }

        return max_area;

    }
};