[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;
    }
};