Zebra_Crossing.cpp

#pragma GCC optimize("Ofast")
#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,avx2,fma")
#pragma GCC optimize("unroll-loops")
#include <bits/stdc++.h>  
#include <complex>
#include <queue>
#include <set>
#include <unordered_set>
#include <list>
#include <chrono>
#include <random>
#include <iostream>
#include <algorithm>
#include <cmath>
#include <string>
#include <vector>
#include <map>
#include <unordered_map>
#include <stack>
#include <iomanip>
#include <fstream>
 
using namespace std;
 
typedef long long ll;
typedef long double ld;
typedef pair<int,int> p32;
typedef pair<ll,ll> p64;
typedef pair<double,double> pdd;
typedef vector<ll> v64;
typedef vector<int> v32;
typedef vector<vector<int> > vv32;
typedef vector<vector<ll> > vv64;
typedef vector<vector<p64> > vvp64;
typedef vector<p64> vp64;
typedef vector<p32> vp32;
ll MOD = 998244353;
double eps = 1e-12;
#define forn(i,e) for(ll i = 0; i < e; i++)
#define forsn(i,s,e) for(ll i = s; i < e; i++)
#define rforn(i,s) for(ll i = s; i >= 0; i--)
#define rforsn(i,s,e) for(ll i = s; i >= e; i--)
#define ln "\n"
#define dbg(x) cout<<#x<<" = "<<x<<ln
#define mp make_pair
#define pb push_back
#define fi first
#define se second
#define INF 2e18
#define fast_cin() ios_base::sync_with_stdio(false); cin.tie(NULL); cout.tie(NULL)
#define all(x) (x).begin(), (x).end()
#define sz(x) ((ll)(x).size())
 

void solve(){
    ll n,k;
    cin>>n>>k;
    string s;
    cin>>s;

    char res = s[0];
    int cnt =0;
    for(int i=1;i<n;i++) {
        if(res != s[i]) {
            cnt++;
            res = s[i];
        }
    }

    if(cnt<k) {
        cout<<-1<<"\n";
        return;
    }
    if(s[0]=='0') {
        if(k%2) {
            for(int i=s.size()-1; i>=0; i--) {
                if(s[i] == '1') {
                    cout<<i+1<<"\n";
                    return;
                }
            }
        }
        else {
            for(int i=s.size()-1; i>=0; i--) {
                if(s[i] == '0') {
                    cout<<i+1<<"\n";
                    return;
                }
            }
        }
    }
    else {
        if(k%2) {
            for(int i=s.size()-1; i>=0; i--) {
                if(s[i] == '0') {
                    cout<<i+1<<"\n";
                    return;
                }
            }
        }
        else {
            for(int i=s.size()-1; i>=0; i--) {
                if(s[i] == '1') {
                    cout<<i+1<<"\n";
                    return;
                }
            }
        }
    }
}
int main()
{
    fast_cin();
    ll t;
    cin >> t;
    for(int it=1;it<=t;it++) {
        solve();
    }
    return 0;
}