如果矩阵A中存在这样的一个元素A[i][j]满足条件“A[i][j]是第i行中值最小的元素，且又是第j列中值最大的元素”，则称之为该矩阵的一个马鞍点。编写一个函

If there is such an element A[i][j] in the matrix A that satisfies the condition "A[i][j] is the element with the smallest value in the i-th row and is the element with the largest value in the j-th column", then Call it a saddle point of the matrix. Write a function that computes all saddle points of matrix A of m*n