C++14 解法, 执行用时: 1ms, 内存消耗: 372KB, 提交时间: 2020-08-21

#include<stdio.h>
#include<string.h>
int main()
{
    char str[1024];
    scanf("%s",str);
    int len = strlen(str);
    int count = 0, max = 0;
    int offset = 1;
    while(len - offset >= max)
    {
        for(int i = 0;i < len - offset;i++)
        {
            if(str[i] == str[i + offset]) count++;
            else
            {
                if(count > max) max = count;
                count = 0;
            }
        }
        offset++;
    }
    if(count > max) max = count;
    printf("%d",max);
    return 0;
}

C 解法, 执行用时: 1ms, 内存消耗: 372KB, 提交时间: 2020-07-16

#include <stdio.h>
#include <string.h>
#include <stdbool.h>
#define max(a, b) ((a) > (b) ? (a) : (b))
char* substr(char *str, int left, int right)
{
    char *res = (char *) malloc((right - left + 1) * sizeof(char));
    for (int i = left; i < right; ++i) {
        res[i - left] = str[i];
    }
    res[right - left] = '\0';
    return res;
}
bool find(char *str, char *sub)
{
    for (int  i = 0; i < strlen(str); ++i) {
        if (strncmp(str + i, sub, strlen(sub)) == 0) {
            return true;
        }
    }
    return false;
}
int main()
{
    char str[1001];
    scanf("%s", str);
    int maxlen = 0;
    int left, right;
    left = 0;
    right = 1;
    while (left <= right && right < strlen(str)) {
        char *s = substr(str, left, right);
        if (find(str + right, s)) {
            maxlen = max(maxlen, right - left);
            ++right;
        } else {
            ++left;
            if (left >= right) {
                ++right;
            }
        }
        free(s);
    }
    printf("%d\n", maxlen);
    return 0;
}