simple approach (travel and see the element)
class Solution {
    public List<Integer> luckyNumbers (int[][] matrix) {
        int row=matrix.length;
        int col=matrix[0].length;
        List<Integer>li=new ArrayList<>();
        for(int i=0;i<row;i++)
        {
            int j=0;
            int mini=Integer.MAX_VALUE;
            int idx=0;
            while(j<col)
            {
                if(matrix[i][j]<mini)
                {
                    mini=matrix[i][j];
                    idx=j;
                }
                j++;
            }
            int p=0;
            boolean res=false;
            while(p<row)
            {
                if(matrix[p][idx]>mini)
                {
                  res=true;
                    break;
                }
                p++;
            }
            if(res==false)
            {
                li.add(mini);
            }
        }
        return li;
    }
}
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