[leetcode] Maximal Square

Problem:

Given a 2D binary matrix filled with 0's and 1's, find the largest square containing all 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 4.

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比较详细的解法在这里:

https://leetcode.com/discuss/38489/easy-solution-with-detailed-explanations-8ms-time-and-space

附上最终的代码:

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