Repeating substring

input/code.cpp: In function 'int main()':
input/code.cpp:13:10: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
     scanf("%100001s", string);
     ~~~~~^~~~~~~~~~~~~~~~~~~~

#include <algorithm>
#include <cstddef>
#include <cstdio>
#include <cstring>
#include <vector>

using std::sort;
using std::vector;


int main() {
    char string[100002];
    scanf("%100001s", string);
    const size_t n = strlen(string);

    vector<size_t> suffixes(n);

    for (size_t i = 0; i < n; i++) {
        suffixes[i] = i;
    }

    auto compare_suffixes = [&string](size_t a, size_t b) {
        return strcmp(&string[a], &string[b]) < 0;
    };

    sort(suffixes.begin(), suffixes.end(), compare_suffixes);

    char* longest_prefix = string;
    size_t longest_prefix_length = 0;

    for (size_t i = 0; i + 1 < n; i++) {
        char* a = &string[suffixes[i]];
        char* b = &string[suffixes[i + 1]];

        size_t j = 0;
        for (; a[j] != 0 && b[j] != 0 && a[j] == b[j]; j++) {
        }

        if (j > longest_prefix_length) {
            longest_prefix = a;
            longest_prefix_length = j;
        }
    }

    longest_prefix[longest_prefix_length] = 0;
    printf("%s\n", longest_prefix);

    return 0;
}

Test 1

Verdict: ACCEPTED

Test 2

Verdict: ACCEPTED

Test 3

Verdict: ACCEPTED

Test 4

Verdict: ACCEPTED

Test 5

Verdict: ACCEPTED

Test 6

Verdict: ACCEPTED

Test 7

Verdict: ACCEPTED

Test 8

Verdict: ACCEPTED

Test 9

Verdict: ACCEPTED

Test 10

Verdict: ACCEPTED

Test 11

Verdict: TIME LIMIT EXCEEDED

Test 12

Verdict: UNKNOWN

Test 13

Verdict: UNKNOWN

Test 14

Verdict: UNKNOWN

Test 15

Verdict: UNKNOWN