func_code_string: #include <bits/stdc++.h>   using namespace std;   unsigned long long int ncr(unsigned long long int a, unsigned long long int b) {     unsigned long long int ans = 1;     for (unsigned long long int i = 1; i <= b; i++) {       ans *= (a - i + 1);     }     for (unsigned long long int i = 1; i <= b; i++) {       ans /= i;     }     return ans;   }   unsigned long long int power(unsigned long long int a,                                unsigned long long int b) {     unsigned long long int ans = 1;     for (int i = 1; i <= b; i++) {       ans *= a;     }     return ans;   }   unsigned long long int solvelessthansingle(int numofdigit) {     unsigned long long int ans = ncr(numofdigit - 1, 1);     ans *= 9;     return ans;   }   unsigned long long int solvelessthandouble(int numofdigit) {     unsigned long long int ans = ncr(numofdigit - 1, 2);     ans *= 81;     return ans;   }   unsigned long long int solvelessthantriple(unsigned long long int numofdigit) {     unsigned long long int ans = ncr(numofdigit - 1, 3);     ans *= 729;     return ans;   }   unsigned long long int solvelessthannone(unsigned long long int numofdigit) {     return 1;   }   unsigned long long int solve(unsigned long long int n,                                unsigned long long int rem) {     if (rem == 0) {       return 0;     }     if (n < 10) {       return n;     }     int numofdigit = 0;     unsigned long long int n2 = n;     while (n2) {       numofdigit++;       n2 /= 10;     }     unsigned long long int ans = 0;     if (rem >= 1) ans += solvelessthansingle(numofdigit);     if (rem >= 2) ans += solvelessthandouble(numofdigit);     if (rem >= 3) ans += solvelessthantriple(numofdigit);     int lastdigit;     unsigned long long int n1 = n;     while (n1) {       int temp = n1 % 10;       lastdigit = temp;       n1 /= 10;     }     if (rem >= 1) ans += (lastdigit)*solvelessthannone(numofdigit);     if (rem >= 2) ans += (lastdigit - 1) * solvelessthansingle(numofdigit);     if (rem >= 3) ans += (lastdigit - 1) * solvelessthandouble(numofdigit);     unsigned long long int mul =         power((unsigned long long int)10, (unsigned long long int)numofdigit - 1);     mul *= lastdigit;     n -= mul;     ans += solve(n, rem - 1);     return ans;   }   int main() {     ios_base::sync_with_stdio(false);     cin.tie(NULL);     int t = 1;     cin >> t;     while (t--) {       unsigned long long int n, m;       cin >> n >> m;       unsigned long long int ans = solve(m, 3) - solve(n - 1, 3);       cout << ans << endl;     }     return 0;   }   