85.最大矩阵

Maximal Rectangle

问题描述

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 0
1 0 1 1 1
1 1 1 1 1
1 0 0 1 0
Return 6.

参考答案

class Solution {
public:
    int maximalRectangle(vector<vector<char> > &matrix) {
        if(matrix.empty()) return 0;
        const int m = matrix.size();
        const int n = matrix[0].size();
        int left[n], right[n], height[n];
        fill_n(left,n,0); fill_n(right,n,n); fill_n(height,n,0);
        int maxA = 0;
        for(int i=0; iint cur_left=0, cur_right=n; 
            for(int j=0; j// compute height (can do this from either side)
                if(matrix[i][j]=='1') height[j]++; 
                else height[j]=0;
            }
            for(int j=0; j// compute left (from left to right)
                if(matrix[i][j]=='1') left[j]=max(left[j],cur_left);
                else {left[j]=0; cur_left=j+1;}
            }
            // compute right (from right to left)
            for(int j=n-1; j>=0; j--) {
                if(matrix[i][j]=='1') right[j]=min(right[j],cur_right);
                else {right[j]=n; cur_right=j;}    
            }
            // compute the area of rectangle (can do this from either side)
            for(int j=0; jreturn maxA;
    }
};

性能：