Benchmark

#include <cstring>      // strlen
#include <algorithm>    // mismatch
#include <cassert>      // assert
#include <cstddef>      // ptrdiff_t
#include <iterator>     // distance

std::ptrdiff_t len_common_prefix_base(char const a[], char const b[])
{
    assert(std::strlen(b) <= std::strlen(a));
    return std::distance(b, std::mismatch(b, b + std::strlen(b), a).first);
}

std::ptrdiff_t len_common_prefix_10x(char const a[], char const b[])
{
    assert(std::strlen(b) <= std::strlen(a));
    using block_type = long long int;

    auto p = reinterpret_cast<block_type const*>(a);
    auto q = reinterpret_cast<block_type const*>(b);

    auto const n = std::strlen(b);
    auto const num_blocks = n / sizeof(block_type);

    auto block_mismatch = std::mismatch(q, q + num_blocks, p);
    auto b2 = reinterpret_cast<char const*>(block_mismatch.first);
    auto a2 = reinterpret_cast<char const*>(block_mismatch.second);

    return std::distance(b, std::mismatch(b2, b + n, a2).first);
}

long long int len_common_prefix(char a[], char b[]) {
    long long int* p = (long long int*)a;
    long long int* q = (long long int*)b;
    int ratio = sizeof(long long int) / sizeof(char);
    while (*p == *q) {
        p++;
        q++;
    }
    long long long_long_diff = p-(long long int*)a;
    char* p2 = (char*)p;
    char* q2 = (char*)q;
    while (*p2 == *q2) {
        p2++;
        q2++;
    }
    return long_long_diff * ratio + (p2 - (char*)p);
}

long long int stringSimilarity(char a[]) {
    long long l = strlen(a);
    long long int sum = l;
    long long int sum_red = 0;
    int ratio = sizeof(long long int) / sizeof(char);
    long long l_red = l / ratio;
    for (long long i = 1; i < l; i++) {
      sum += len_common_prefix(a, a +i);
    }
    return sum;
}

int main() {
  int t, i;
  scanf("%d",&t);
  char a[100001];
  for (i=0;i<t;i++) {
    scanf("%s",a);
    long long int res=stringSimilarity(a);
    printf("%lld\n",res);
  }
  return 0;
}