What is problem in this sbumatrix approach 2;

#1
#2

There will be three corner cases for prefix sum from (li,lj) to (bi,bj).

                 if(li==0 && lj==0){
                    sum=sum+a[bi][bj];
                }
                else if(li==0){
                    sum = a[bi][bj]-a[bi][lj-1];
                }
                else if(lj==0){
                    sum = a[bi][bj]-a[li-1][bj];
                }
                else{
                    sum = a[bi][bj]-a[bi][lj-1]-a[li-1][bj]+a[li-1][lj-1];
                }

You can easily understand these by just drawing them for some matrix example.

#3

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