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https://blog.csdn.net/u011328934/article/details/36409469

option=com_onlinejudge&Itemid=8&page=show_problem&category=474&problem=2828&mosmsg=Submission+received+with+ID+13820744" rel="nofollow">题目链接：uva 11728 - Alternate
Task

题目大意：给出S，求N，要求N全部的因子和为S。

解题思路：枚举因子i，全部整除i的数和加上i。

#include <cstdio>

#include <cstring>

const int N = 1005;

int n, c[N], v[N];

void init () {

    memset(c, 0, sizeof(c));

    memset(v, -1, sizeof(v));

    for (int i = 1; i < N; i++) {

        for (int j = i; j < N; j += i)

            c[j] += i;

        if (c[i] < N)

            v[c[i]] = i;

    }

}

int main () {

    init();

    int cas  = 1;

    while (scanf("%d", &n) == 1 && n) {

        printf("Case %d: %d\n", cas++, v[n]);

    }

    return 0;

}