String Sort Question only one test case is passing and other is showing run error pls help

https://online.codingblocks.com/app/player/161395/content/158307/4738/code-challenge

Use C++ inbuilt sort function with a custom comparator something like this:

bool mycompare( string a, string b)
{
int l1=a.length();int l2=b.length();int flag=-1;
for(int i=0;i<min(l1,l2);i++){
if(a[i]!=b[i])
flag=0;
}
if(flag==-1) // means there is a prefix match
return l1>l2; // so sort decreasing order of length
else
return a<b; //sorting in normal dictionary order when no prefix match
}

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