div 2 c Binary String Copying

#include<bits/stdc++.h>
using namespace std ;
using ll = long long;
using PII = pair<int,int>;
string s;
void solve(){
    int n,m;
    cin >> n >> m;
    //vector<int>s(n+1);
    vector<int>ne1(n+2,n+1);
    vector<int>pre0(n+2,0);
    cin>>s;
    s = " " + s;
    for(int i=1;i<=n;i++){
        pre0[i] = pre0[i-1];
        if(s[i] == '0'){
            pre0[i] = i;
        }
    }
    for(int i=n;i>=1;i--){
        ne1[i] = ne1[i+1];
        if(s[i] == '1'){
            ne1[i] = i;
        }
    }
    set<PII> s;
    while(m--){
        int l,r;
        cin>>l>>r;
        //cout<<ne1[l]<<" "<<pre0[r]<<endl;
        if(ne1[l] > pre0[r]){
            s.emplace(-1,-1);
        }else{
            s.emplace(ne1[l],pre0[r]);
        }
    }
    cout<<s.size();

}



int main(){
    int t;
    cin>>t;
    while(t--){
        solve();
        puts("");
    }
}

用最小的变换区间代表整个大区间

找到L右边最近的1 R左边最近的0 变换区间就在这两个之间