leetcode221 Maximal Square

思路：

dp。

实现：

class Solution 
{
public:
    int maximalSquare(vector<vector<char>>& matrix) 
    {
        if (matrix.empty()) return 0;
        int m = matrix.size(), n = matrix[0].size();
        vector<int> dp(m, 0);
        int maxn = 0;
        for (int i = 0; i < m; i++)
        {
            dp[i] = matrix[i][0] - '0';
            maxn = max(maxn, dp[i]);
        }
        for (int i = 1; i < n; i++)
        {
            int pre = dp[0];
            dp[0] = matrix[0][i] - '0';
            maxn = max(dp[0], maxn);
            for (int j = 1; j < m; j++)
            {
                if (matrix[j][i] == '1')
                {
                    pre = min(pre, min(dp[j - 1], dp[j])) + 1;
                    swap(dp[j], pre);
                    maxn = max(maxn, dp[j]);
                }
                else dp[j] = 0;
            }
        }
        return maxn * maxn;
    }
};