Solved problem 1017D from codeforces

Author: AliOsm

CodeForces/1017D. The Wu.cpp

@@ -0,0 +1,59 @@
+/*
+  Idea:
+    - Precalculate the frequency of each element in the multiset S.
+    - Precalculate the cost of each mask from 0 to 2^n.
+    - Precalculate the number of elements for each pair (i, j)
+      that has `k` as cost.
+    - Prefix sum the previous point.
+    - Answer the queries in O(n).
+*/
+
+#include <bits/stdc++.h>
+
+using namespace std;
+
+int const N = 12;
+char s[13];
+int n, m, q, k, a[N], c[1 << N], fr[1 << N], all[1 << N][1201];
+
+int main() {
+  scanf("%d %d %d", &n, &m, &q);
+  for(int i = 0; i < n; ++i)
+    scanf("%d", a + i);
+  for(int i = 0, tmp; i < m; ++i) {
+    scanf("%s", s);
+    tmp = 0;
+    for(int j = 0; j < n; ++j)
+      tmp |= ((s[j] - '0') << (n - j - 1));
+    ++fr[tmp];
+  }
+
+  for(int i = 0; i < (1 << n); ++i)
+    for(int j = 0; j < n; ++j)
+      if(((i >> j) & 1) != 0)
+        c[i] += a[n - j - 1];
+
+  for(int i = 0; i < (1 << n); ++i)
+    for(int j = 0, x; j < (1 << n); ++j) {
+      x = 0;
+      for(int l = 0; l < n; ++l)
+        if(((i >> l) & 1) == ((j >> l) & 1))
+          x |= (1 << l);
+
+      all[i][c[x]] += fr[j];
+    }
+
+  for(int i = 0; i < (1 << n); ++i)
+    for(int j = 1; j < 1201; ++j)
+      all[i][j] += all[i][j - 1];
+
+  for(int i = 0, cur; i < q; ++i) {
+    scanf("%s %d", s, &k);
+    cur = 0;
+    for(int j = 0; j < n; ++j)
+      cur |= ((s[j] - '0') << (n - j - 1));
+    printf("%d\n", all[cur][k]);
+  }
+
+  return 0;
+}

CodeForces/README.md

@@ -551,6 +551,7 @@
 - [1016B. Segment Occurrences](http://codeforces.com/contest/1016/problem/B)
 - [1016C. Vasya And The Mushrooms](http://codeforces.com/contest/1016/problem/C)
 - [1016D. Vasya And The Matrix](http://codeforces.com/contest/1016/problem/D)
+- [1017D. The Wu](https://codeforces.com/contest/1017/problem/D)
 - [1020A. New Building for SIS](http://codeforces.com/contest/1020/problem/A)
 - [1020B. Badge](http://codeforces.com/contest/1020/problem/B)
 - [1020C. Elections](http://codeforces.com/contest/1020/problem/C)