divisible por 3

Author: Noodle96

Free/divisiblePor3.cpp

@@ -0,0 +1,121 @@
+#include <bits/stdc++.h>
+#define all(x) x.begin(),x.end()
+#define msg(str,str2) cout << str << str2<< endl
+using namespace std;
+
+using ll = long long;
+using ld = long double;
+using uint = unsigned int;
+using ull = unsigned long long;
+template<typename T>
+using pair2 = pair<T, T>;
+using pii = pair<int, int>;
+using pli = pair<ll, int>;
+using pll = pair<ll, ll>;
+
+#define pb push_back
+#define mp make_pair
+
+int gcd(int a,int b){
+	if(a%b==0) return b;
+	else return gcd(b,a%b);
+}
+
+clock_t startTime;
+double getCurrentTime() {
+	return (double)(clock() - startTime) / CLOCKS_PER_SEC;
+}
+
+void solve(){
+    int n; cin>>n;
+    string s; cin>>s;
+    vector<int> vec(n);
+    for(int e = 0 ; e < n; e++){
+        vec[e] = s[e] - '0';
+    }
+   
+    //  for(int e = 0 ; e <n; e++){
+    //     cout << vec[e]<< " ";
+    // }cout << endl;
+
+    // prefix sum
+    for(int e = 1 ; e <n; e++){
+        vec[e] = vec[e-1]+ vec[e];
+    }
+
+    //  for(int e = 0 ; e <n; e++){
+    //     cout << vec[e]<< " ";
+    // }cout << endl;
+    vector<int> modulo3(n);
+    for(int e = 0 ;e < n ; e++){
+        modulo3[e] = vec[e]%3;
+    }
+    vector<int> ceros(n),unos(n),dos(n);
+    //ceros
+    if(modulo3[0] == 0) ceros[0] = 1;
+    else ceros[0] = 0;
+    for(int e = 1 ; e < n; e++){
+        if(modulo3[e] == 0){
+            ceros[e] = ceros[e-1] +1;
+        }else{
+            ceros[e] = ceros[e-1] + 0;
+        }
+    }
+    //unos
+    if(modulo3[0] == 1) unos[0] = 1;
+    else unos[0] = 0;
+    for(int e = 1 ; e < n; e++){
+        if(modulo3[e] == 1){
+            unos[e] = unos[e-1] +1;
+        }else{
+            unos[e] = unos[e-1] + 0;
+        }
+    }
+    //dos
+    if(modulo3[0] == 2) dos[0] = 1;
+    else dos[0] = 0;
+    for(int e = 1 ; e < n; e++){
+        if(modulo3[e] == 2){
+            dos[e] = dos[e-1] +1;
+        }else{
+            dos[e] = dos[e-1] + 0;
+        }
+    }
+    // cout << "prints:" << endl;
+    // for(int e = 0 ; e < n; e++){
+    //     cout << ceros[e] << " ";
+    // }cout << endl;
+    // for(int e = 0 ; e < n; e++){
+    //     cout << unos[e] << " ";
+    // }cout << endl;
+
+    // for(int e = 0 ; e < n; e++){
+    //     cout << dos[e] << " ";
+    // }cout << endl;
+
+    int cont = 0;
+    for(int e = 1 ;e < n ; e++){
+        if(vec[e]%3 ==  0){
+            cont += ceros[e-1];
+        }else if(vec[e]%3==1){
+            cont += unos[e-1];
+        }else{
+            // vec[e]%3==2
+            cont += dos[e-1];
+        }
+    }
+    for(int e = 0;e < n ; e++){
+        if(vec[e]%3==0) cont++;
+    }
+    cout <<   cont << endl;
+
+
+}
+
+int main(){
+	ios_base::sync_with_stdio(false);
+	cin.tie(0);
+    int t; cin>>t;
+    while(t--)solve();
+	return 0;
+}