[LeetCode]Maximal Rectangle

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

思考：跟上一题一样，维护左右边界。参考：http://discuss.leetcode.com/questions/260/maximal-rectangle#

class Solution {

public:

    int maximalRectangle(vector<vector<char> > &matrix) {

        if (matrix.empty()) {

            return 0;

        }



        int n = matrix[0].size();

        vector<int> H(n);

        vector<int> L(n);

        vector<int> R(n, n);



        int ret = 0;

        for (int i = 0; i < matrix.size(); ++i) {

            int left = 0, right = n;

            // calculate L(i, j) from left to right

            for (int j = 0; j < n; ++j) {

                if (matrix[i][j] == '1') {

                    ++H[j];

                    L[j] = max(L[j], left);

                }

                else {

                    left = j+1;

                    H[j] = 0; L[j] = 0; R[j] = n;

                }

            }

            // calculate R(i, j) from right to right

            for (int j = n-1; j >= 0; --j) {

                if (matrix[i][j] == '1') {

                    R[j] = min(R[j], right);

                    ret = max(ret, H[j]*(R[j]-L[j]));

                }

                else {

                    right = j;

                }

            }

        }



        return ret;

    }

};