378. 有序矩阵中第K小的元素

class Solution {
public:
    int kthSmallest(vector<vector<int>>& matrix, int k) {
        for (int i = 0; i < k-1; i++)
        {
            pop(matrix);
        }
        return matrix[0][0];
    }
   
   
    void swap(std::vector<std::vector<int>>& matrix, int i, int j, int ii, int jj)
    {
        int tmp = matrix[i][j];
        matrix[i][j] = matrix[ii][jj];
        matrix[ii][jj] = tmp;
    }

    void pop(std::vector<std::vector<int>>& matrix)
    {
        int n = matrix.size();

        int i = 0;
        int j = 0;

        matrix[i][j] = INT_MAX;

        while (i < n - 1 || j < n - 1)
        {
            int a = INT_MAX;
            if (i < n - 1)
            {
                a = matrix[i + 1][j];
            }
            int b = INT_MAX;
            if (j < n - 1)
            {
                b = matrix[i][j + 1];
            }

            if (a == b && a == INT_MAX)
            {
                break;
            }

            if (a < b)
            {
                swap(matrix, i, j, i + 1, j);
                i++;
            }
            else
            {
                swap(matrix, i, j, i, j + 1);
                j++;
            }
        }
    }
};