func_code_string: #include <bits/stdc++.h>   using namespace std;   struct Ev {     int pos;     bool st;     Ev(int pos, bool st) : pos(pos), st(st) {}     inline bool operator<(const Ev &rhs) const { return pos < rhs.pos; }   };   int n, k;   vector<Ev> ev;   int f[200005], rf[200005];   const int MOD = 1e9 + 7;   int c(int n, int k) { return (long long)f[n] * rf[k] % MOD * rf[n - k] % MOD; }   int binPow(long long x, int p) {     long long res = 1;     while (p) {       if (p & 1) res = res * x % MOD;       p >>= 1;       if (p) x = x * x % MOD;     }     return (int)res;   }   int main() {     f[0] = rf[0] = 1;     for (int i = 1; i < 200005; ++i) {       f[i] = (long long)f[i - 1] * i % MOD;       rf[i] = binPow(f[i], MOD - 2);     }     scanf( %d%d , &n, &k);     for (int i = 0; i < (int)(n); ++i) {       int from, to;       scanf( %d%d , &from, &to);       ev.push_back(Ev(from, true));       ev.push_back(Ev(to + 1, false));     }     int pre = -1e9 - 1234;     sort(ev.begin(), ev.end());     int cnt = 0;     int ans = 0;     for (Ev e : ev) {       if (cnt >= k) {         ans = (ans + (long long)c(cnt, k) * (e.pos - pre)) % MOD;       }       pre = e.pos;       if (e.st)         ++cnt;       else         --cnt;     }     printf( %d n , ans);     return 0;   }   