参考答案： #include <stdio.h> #include <string.h> #define MAXN 1000000 char str[MAXN]; int main() { scanf("%s", str); for (long i = strlen(str) - 1; i >= 0; --i) { long count = 0; while (count <= i - count && str[count] == str[i - count]) { count++; } if (count > i - count) { printf("%ld\n", i + 1); break; } } }