子矩阵求和问题

两道类似的子矩阵求和问题，都是化二维为一维去做，一维子数组求和问题有：和为K的子数组个数、最大子数组和，二维子矩阵求可以使用同样的方法。

1074. 元素和为目标值的子矩阵数量

class Solution {
public:
    int numSubmatrixSumTarget(vector>& matrix, int target) {
        int row[300] = {0};
        unordered_map mp;
        int ans = 0, m = matrix.size(), n = matrix[0].size();
        for(int i = 0; i < m; i++)
        {
            memset(row, 0, sizeof(row));
            for(int j = i; j < m; j++)
            {
                for(int k = 0; k < n; k++) row[k] += matrix[j][k];
                mp.clear();
                mp[0] = 1;
                int sum = 0;
                for(int k = 0; k < n; k++)
                {
                    sum += row[k];
                    auto it = mp.find(sum - target);
                    if(it != mp.end()) ans += it->second;
                    mp[sum]++;
                }
            }
        }
        return ans;
    }
};

面试题 17.24. 最大子矩阵

class Solution {
public:
    vector getMaxMatrix(vector>& matrix) {
        int r1, c1, r2, c2;
        int m = matrix.size(), n = matrix[0].size();
        int maxsum = INT32_MIN;
        int row[200];
        for(int i = 0; i < m; i++)
        {
            memset(row, 0, sizeof(row));
            for(int j = i; j < m; j++)
            {
                for(int k = 0; k < n; k++) row[k] += matrix[j][k];
                int sum = 0, sc = 0;
                for(int k = 0; k < n; k++)
                {
                    sum += row[k];
                    if(sum > maxsum)
                    {
                        maxsum = sum;
                        r1 = i;
                        r2 = j;
                        c1 = sc;
                        c2 = k;
                    }
                    if(sum < 0)
                    {
                        sum = 0;
                        sc = k + 1;
                    }
                }
            }
        }
        return {r1, c1, r2, c2};
    }
};