Solved problem 1029D from codeforces

Author: AliOsm

CodeForces/1029D. Concatenated Multiples.cpp

@@ -0,0 +1,48 @@
+#include <bits/stdc++.h>
+
+using namespace std;
+
+int const N = 2e5 + 1;
+int n, k, a[N];
+long long p[11];
+vector<long long> rem[11];
+
+int main() {
+  p[0] = 1;
+  for(int i = 1; i < 11; ++i)
+    p[i] = p[i - 1] * 10;
+
+  scanf("%d %d", &n, &k);
+  for(int i = 0; i < n; ++i)
+    scanf("%d", a + i);
+
+  for(int i = 0; i < n; ++i)
+    rem[int(floor(log10(a[i])) + 1)].push_back(a[i] % k);
+
+  for(int i = 1; i <= 10; ++i)
+    sort(rem[i].begin(), rem[i].end());
+
+  long long res = 0;
+  for(int i = 0, l, r; i < n; ++i) {
+    for(int j = 1; j <= 10; ++j) {
+      if(rem[j].empty())
+        continue;
+
+      long long tmp = (k - ((1ll * (a[i] % k) * (p[j] % k)) % k)) % k;
+      if(tmp < 0)
+        continue;
+
+      l = lower_bound(rem[j].begin(), rem[j].end(), tmp) - rem[j].begin();
+      r = upper_bound(rem[j].begin(), rem[j].end(), tmp) - rem[j].begin();
+
+      res += r - l;
+    }
+
+    if((1ll * ((a[i] % k) * (p[int(floor(log10(a[i])) + 1)] % k)) % k + a[i]) % k == 0)
+      --res;
+  }
+
+  printf("%lld\n", res);
+
+  return 0;
+}

CodeForces/README.md

@@ -564,3 +564,4 @@
 - [1029A. Many Equal Substrings](http://codeforces.com/contest/1029/problem/A)
 - [1029B. Creating the Contest](http://codeforces.com/contest/1029/problem/B)
 - [1029C. Maximal Intersection](http://codeforces.com/contest/1029/problem/C)
+- [1029D. Concatenated Multiples](http://codeforces.com/contest/1029/problem/D)