E - Strange Operation

https://codeforces.com/contest/1383/submission/190440602

Codeforces/1383/E/E.cpp

@@ -0,0 +1,57 @@
+#include <iostream>
+#include <algorithm>
+#include <string>
+
+using std::cin;
+using std::cout;
+const char endl = '\n';
+
+const int N = 1e6 + 5;
+const int mod = 1e9 + 7;
+
+int n, cnt = 1,
+       pre[N], w[N], sum[N], f[N];
+std::string s;
+
+int main() {
+    std::ios::sync_with_stdio(false);
+    cin.tie(nullptr);
+
+    cin >> s;
+
+    n = s.size();
+
+    for (char c : s) {
+        if (c == '0') pre[cnt]++;
+        else cnt++;
+    }
+
+    if (cnt == 1) {
+        cout << n << endl;
+
+        exit(0);
+    }
+
+    std::fill(w, w + 1 + n, 1);
+
+    sum[1] = f[1] = 1;
+
+    for (int i = 2; i < cnt; i++) {
+        int l = w[0];
+
+        for (int j = 0; j <= pre[i]; j++) {
+            l = w[j];
+            f[i] = (static_cast<long long>(f[i]) + sum[i - 1] - sum[l - 1] + mod) % mod;
+        }
+
+        for (int j = 0; j <= pre[i]; j++) {
+            w[j] = i;
+        }
+
+        sum[i] = (static_cast<long long>(sum[i - 1]) + f[i]) % mod;
+    }
+
+    cout << static_cast<long long>(pre[1] + 1) * (pre[cnt] + 1) % mod * sum[cnt - 1] % mod << endl;
+
+    return 0;
+}