以下相同代码，开启o2优化，就只能通过5个点，会把所有全都判成'lucky word'，而关闭o2优化，能AC。这是为啥？

#include <stdio.h>
#include <string.h>
int sushu(int i){
	int ss[25]={2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97};
	for(int j=0;j<=25;j++){
		if(i==ss[j]){
			return 1;
		}
	}
	return 0;
	}

int main() {
	char x[1000];
	gets(x);
	int n = strlen(x);
	int alpha_count[1000] = {0};
	for (int i = 0; i < n; i++) {
		alpha_count[x[i]]++;
	}
	int min = 100, max = 0;
	for (int i = 'a'; i <= 'z'; i++) {
		if (alpha_count[i]) {
			min = alpha_count[i] < min ? alpha_count[i] : min;
			max = alpha_count[i] > max ? alpha_count[i] : max;
		}
	}
	int ret = max-min;
	printf("%s\n%d", sushu(ret)?"Lucky Word":"No Answer",sushu(ret)?ret:0);
	return 0;
}