Language: C++

#pragma GCC optimize("O3")
#include <bits/stdc++.h>
#define ll long long
#define rep2(i,a,b) for(ll i=a;i<=b;++i)
#define rep(i,n) for(ll i=0;i<n;i++)
#define rep3(i,a,b) for(ll i=a;i>=b;i--)
#define pii pair<int,int>
#define pll pair<ll,ll>
#define pq priority_queue
#define pb push_back
#define eb emplace_back
#define vec vector<int>
#define vecll vector<ll>
#define vecpii vector<pii>
#define vec2(a,b) vector<vec>(a,vec(b))
#define vec2ll(a,b) vector<vecll>(a,vecll(b))
#define vec3(a,b,c) vector<vector<vec>>(a,vec2(b,c))
#define vec3ll(a,b,c) vector<vector<vecll>>(a,vec2ll(b,c))
#define fi first
#define se second
#define endl "\n"
#define all(c) begin(c),end(c)
#define ios ios_base::sync_with_stdio(0),cin.tie(0),cout.tie(0);
#define lb(c,x) distance(c.begin(),lower_bound(all(c),x))
#define ub(c,x) distance(c.begin(),upper_bound(all(c),x))
#define MM " "
// #define INF 100000000
using namespace std;
int in() {int x;cin>>x;return x;}
ll lin() {ll x;cin>>x;return x;}
string stin() {string s;cin>>s;return s;}
template<class T> inline bool chmax(T& a,T b){if(a<b){a=b;return 1;}return 0;}
template<class T> inline bool chmin(T& a,T b){if(a>b){a=b;return 1;}return 0;}
template<class T> inline void print(pair<T,T> p){cout<<"("<<p.first<<","<<p.second<<") ";}
template<class T> inline void print(vector<pair<T,T>> v){for(auto e:v)print(e); cout<<endl;}
template<class T> inline void print(T v){for(auto e:v)cout<<e<<" ";cout<<endl;}

const ll MOD=1e9+7;
const int N=1100000;
 
template <ll Modulus> class modint {
  using u64 = ll;
 
public:
  u64 a;
 
  constexpr modint(const u64 x = 0) noexcept : a(((x % Modulus) + Modulus)%Modulus) {}
  constexpr u64 &value() noexcept { return a; }
  constexpr const u64 &value() const noexcept { return a; }
  constexpr modint operator+(const modint rhs) const noexcept {
    return modint(*this) += rhs;
  }
  constexpr modint operator-(const modint rhs) const noexcept {
    return modint(*this) -= rhs;
  }
  constexpr modint operator*(const modint rhs) const noexcept {
    return modint(*this) *= rhs;
  }
  constexpr modint operator/(const modint rhs) const noexcept {
    return modint(*this) /= rhs;
  }
  constexpr modint &operator+=(const modint rhs) noexcept {
    a += rhs.a;
    if (a >= Modulus) {
      a -= Modulus;
    }
    return *this;
  }
  constexpr modint &operator-=(const modint rhs) noexcept {
    if (a < rhs.a) {
      a += Modulus;
    }
    a -= rhs.a;
    return *this;
  }
  constexpr modint &operator*=(const modint rhs) noexcept {
    a = a * rhs.a % Modulus;
    return *this;
  }
  constexpr modint &operator/=(modint rhs) noexcept {
    u64 exp = Modulus - 2;
    while (exp) {
      if (exp % 2) {
        *this *= rhs;
      }
      rhs *= rhs;
      exp /= 2;
    }
    return *this;
  }
};
 
#define mint modint<MOD>
mint inv[N],comb[N],prd[N],invprd[N];
void calc_inv(){
    inv[1]=1;
    rep2(i,2,N-1){
        inv[i]=inv[MOD%i]*(-MOD/i);
    }
    return;
}
void calc_product(){
    prd[0]=prd[1]=1;
    invprd[0]=invprd[1]=1;
    rep2(i,2,N-1){
        prd[i]=prd[i-1]*i;
        invprd[i]=inv[i]*invprd[i-1];
    }
    return ;
}
mint cmb(int a,int b){
    if(a<b)return 0;
    if(a<0||b<0)return 0;
    return {prd[a]*invprd[b]*invprd[a-b]};
}
mint modpow(mint x,ll n){
    if(n==0) return 1;
    mint res=modpow(x*x,n/2);
    if(n&1) res=res*x;
    return res;
}
void calc(){calc_inv();calc_product();}
using vmint = vector<mint> ;
void print(vmint v){
    for(auto e:v)cout<<e.a<<" ";
    cout<<endl;
}

int main(){
    ios_base::sync_with_stdio(0),cin.tie(0),cout.tie(0);cout<<fixed<<setprecision(15);
    int n=in(),m=in();
    calc();
    string s;cin>>s;
    vec a;
    a.pb(0);
    for(auto e:s){
        a.pb(a.back()+(e=='1'));
    }
    vecpii v;
    rep(i,m){
        int l=in(),r=in();
        if(!v.empty() and v.back().fi==l)chmax(v.back().se,r);
        else if(!v.empty() and v.back().se>=r) continue;
        else v.eb(l,r);
    }
    v.eb(n+1,n+1);
    vmint dp(n+1);
    dp[0]=1;
    int prel=0,prer=0;
    rep(i,v.size()-1){
        int x = v[i+1].fi-1 , y = v[i].se;
        vmint next(n+1);
        if(v[i+1].fi>v[i].se){
            int l = a[y];
            rep2(j,prel,prer){
                next[l]+=dp[j]*cmb(v[i].se-v[i].fi+1,l-j);
            }
            dp=vmint(n+1);
            dp[a[v[i+1].fi-1]]=next[l];
            prel=prer=a[v[i+1].fi-1];
            continue;
        }
        rep2(j,prel,prer){
            int l = max((int)j,x-y+a[y]);
            int r = min((int)j+x-v[i].fi+1,a[y]);
            rep2(k,l,r){
                next[k]+=dp[j]*cmb(x-v[i].fi+1,k-j);
            }
        }
        dp=next;
        prel=l,prer=r;
    }
    cout<<dp[a[n]].a<<endl;
}




Compiler output:
a.cc: In function 'int main()':
a.cc:171:14: error: 'l' was not declared in this scope
  171 |         prel=l,prer=r;
      |              ^
a.cc:171:21: error: 'r' was not declared in this scope
  171 |         prel=l,prer=r;
      |                     ^