[cses] Add C++ solution for 1660 - Subarray Sums I

Author: abeaumont

cses/1660-1.ans

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+3

cses/1660-1.in

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+5 7
+2 4 1 2 7

cses/1660.cc

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+// https://cses.fi/problemset/task/1660/
+#include <bits/stdc++.h>
+
+using namespace std;
+
+int main() {
+  int n, x, j = 0, k = 0, c = 0, s = 0;
+  cin >> n >> x;
+  vector<int> a(n);
+  for (int i = 0; i < n; i++) cin >> a[i];
+  while (j < n) {
+    if (s < x) {
+      if (k >= n) break;
+      s += a[k++];
+    }
+    else if (s > x) s -= a[j++];
+    else {
+      s -= a[j++];
+      s += a[k++];
+    }
+    if (s == x) c++;
+  }
+  cout << c << endl;
+}