Codeforces Round #795 (Div. 2) C. Sum of Substrings

• Time : O(n)
• Space : O(1)

c++

#include <bits/stdc++.h>

#pragma optimization_level 3
#pragma GCC optimize("Ofast,no-stack-protector,unroll-loops,fast-math,O3")
#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx")
#pragma GCC optimize("Ofast")//Comment optimisations for interactive problems (use endl)
#pragma GCC target("avx,avx2,fma")
#pragma GCC optimization ("unroll-loops")

#define MAX_N 50505
#define INF 987654321
#define EPS 1e-9
#define ll long long
#define pll pair<ll, ll>
#define vpll vector<pll>
#define vall3 vector<array<ll,3>>
#define all3 array<ll,3>
#define all5 array<ll,5>
#define vall5 vector<all5>
#define vll vector<ll>
#define vs vector<string>
#define usll unordered_set<ll>
#define vvs vector<vs>
#define vvll vector<vll>
#define all(a) begin(a), end(a)

using namespace std;

ll solve(string& s, int k) {
    int n = s.length();
    for(int i = n - 1, kk = k; i >= 0 and kk >= 0; i--, kk--) {
        if(s[i] == '0') continue;
        swap(s[i], s[n - 1]);
        k = kk;
        break;
    }
    for(int i = 0, kk = k; i < n - 1 and kk >= 0; i++, kk--) {
        if(s[i] == '0') continue;
        swap(s[i], s[0]);
        k = kk;
        break;
    }

    ll res = 0;
    for(int i = 0; i < n - 1; i++) {
        if(s[i] == '1') res += 10;
        if(s[i + 1] == '1') res += 1;
    }
    return res;
}

int main() {
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    ll tc;
    cin>>tc;
    for(ll i = 1; i <= tc; i++) {
        ll _, k;
        string s;
        cin>>_>>k;
        cin>>s;
        cout<<solve(s, k)<<endl;
    }
    return 0;
}