PAT (Advanced Level) Practise 1120

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本文介绍了一种名为“友数”的算法概念，通过计算整数各位数字之和来判断两个数是否为友数，并统计给定整数集合中不同的友数ID数量及具体ID值。文章提供了完整的C语言实现代码。

PAT (Advanced Level) Practise 1120

1120. Friend Numbers (20)

Two integers are called “friend numbers” if they share the same sum of their digits, and the sum is their “friend ID”. For example, 123 and 51 are friend numbers since 1+2+3 = 5+1 = 6, and 6 is their friend ID. Given some numbers, you are supposed to count the number of different friend ID’s among them. Note: a number is considered a friend of itself.

Input Specification:

Each input file contains one test case. For each case, the first line gives a positive integer N. Then N positive integers are given in the next line, separated by spaces. All the numbers are less than 104.

Output Specification:

For each case, print in the first line the number of different frind ID’s among the given integers. Then in the second line, output the friend ID’s in increasing order. The numbers must be separated by exactly one space and there must be no extra space at the end of the line.

Sample Input:
8
123 899 51 998 27 33 36 12
Sample Output:
4
3 6 9 26

编程实现

#include <stdio.h>

int cal_friendID(int num)
{
    int friendID = 0;

    while ( num ) {
        friendID += num%10;
        num /= 10;
    }
    return friendID;
}

int main(void)
{
    int friendID_counts[37] = {0}; /* 9+9+9+9 */
    int friendID, count = 0;
    int i, n, num;
    int flag = 1;

    scanf("%d", &n);
    for ( i = 0; i < n; i++ ) {
        scanf("%d", &num);
        friendID = cal_friendID(num);
        if ( !friendID_counts[friendID] ) 
            count++;
        friendID_counts[friendID]++;
    }
    printf("%d\n", count);
    for ( i = 0; i < 37; i++ ) {
        if ( friendID_counts[i] ) {
            if ( flag ) {
                printf("%d", i);
                flag = 0;
            } else 
                printf(" %d", i);
        }
    }
    printf("\n");

    return 0;
}