Today I solved problem E. A Simple task that was given at last contest,and I find something intersting and new for me, posible and for other users.Why if I declare k as a global variable I get TLE on test 9 and if I declare as a local variable int k=x my code past all tests?

Can someone explain why?

k=x;
for (l=26;l>=1;l--) {
    st=lower_bound(g[l].begin(),g[l].end(),x)-g[l].begin();
    dr=upper_bound(g[l].begin(),g[l].end(),y)-g[l].begin();
    for (;st<dr;st++) {
         g[l][st]=k; k++;
    }
}

get TLE;

int k=x;
for (int l=26;l>=1;l--) {
    int st=lower_bound(g[l].begin(),g[l].end(),x)-g[l].begin();
    int dr=upper_bound(g[l].begin(),g[l].end(),y)-g[l].begin();
    for (;st<dr;st++) {
         g[l][st]=k; k++;
    }
}

past all tests.