#include "stdio.h" long reverse(long i) { long m, j=0; m = i; while(m){ j = j*10 + m%10; m = m/10; } return j; } long isCircle(long n) { long m; m = reverse(n); if(m != n) return isCircle(m)+1; else return 1; } void palindrome(long low,long high) { long i; for(i=low;i<=high;i++) { if(isCircle(i) == 3) printf("%ld ",i); } } int main() { printf("The palindrome numbers between 11～999 are\n"); palindrome(11,999); return 0; }优化代码

可以考虑在判断回文数的时候，直接计算各个数位上的数字之和，判断这个数字之和是否是回文数，这样就不需要多次调用 `reverse` 函数了。

代码如下：

#include "stdio.h"

long isPalindrome(long n) {
    long sum = 0, m = n;
    while (m) {
        sum = sum * 10 + m % 10;
        m /= 10;
    }
    return sum == n;
}

long isCircle(long n) {
    long sum = 0, m = n;
    while (m) {
        sum += m % 10;
        m /= 10;
    }
    return isPalindrome(sum);
}

void palindrome(long low, long high) {
    long i;
    for (i = low; i <= high; i++) {
        if (isCircle(i)) {
            printf("%ld ", i);
        }
    }
}

int main() {
    printf("The palindrome numbers between 11～999 are\n");
    palindrome(11, 999);
    return 0;
}