func_code_string: #include <bits/stdc++.h>   using namespace std;   char a[500001 + 10], b[500001 + 10], s[(500001 << 1) + 10];   int n, m;   struct BIT {     long long c[500001 << 1];     long long query(int x) {       if (x <= 0) return 0;       long long ans = 0;       for (int i = x; i; i -= (i & -i)) ans += c[i];       return ans;     }     void add(int x, long long p) {       if (x <= 0) x = 1;       for (int i = x; i <= 1000000; i += (i & -i)) c[i] += p;     }   } b1, b2;   int za[500001 * 3], zb[500001 * 3];   char mod[500001 * 3];   void zfunc(char *s, int n, int *z) {     int l = 0, r = 0;     z[1] = n;     int pt;     for (int i = 2; i <= n; ++i) {       if (r < i) {         for (pt = i; pt <= n && s[pt] == s[pt - i + 1]; ++pt)           ;         --pt;         z[i] = pt - i + 1;         if (z[i]) l = i, r = pt;       } else {         int b = r - i + 1, i_ = i - l + 1;         if (z[i_] < b)           z[i] = z[i_];         else {           for (pt = r + 1; pt <= n && s[pt] == s[pt - i + 1]; ++pt)             ;           --pt;           z[i] = pt - i + 1;           l = i, r = pt;         }       }     }   }   int main() {     scanf( %d%d , &n, &m);     scanf( %s%s%s , a + 1, b + 1, s + 1);     memcpy(mod + 1, s + 1, m - 1);     mod[m] =  $ ;     memcpy(mod + m + 1, a + 1, n);     zfunc(mod, n + m, za);     for (int i = 1; i <= n; ++i) za[i] = za[i + m];     reverse(s + 1, s + 1 + m);     reverse(b + 1, b + 1 + n);     memcpy(mod + 1, s + 1, m - 1);     mod[m] =  $ ;     memcpy(mod + m + 1, b + 1, n);     zfunc(mod, n + m, zb);     for (int i = 1; i <= n; ++i) zb[i] = zb[i + m];     reverse(zb + 1, zb + 1 + n);     int cur = 1;     long long ans = 0;     for (int i = 1; i <= n; ++i) {       while (cur <= min(i + m - 2, n))         b1.add(m - 1 - zb[cur], 1), b2.add(m - 1 - zb[cur], zb[cur]), ++cur;       ans += 1ll * b1.query(za[i]) * (za[i] - m + 1) + b2.query(za[i]);       b1.add(m - 1 - zb[i], -1), b2.add(m - 1 - zb[i], -zb[i]);     }     printf( %lld n , ans);     return 0;   }   