【HDOJ】1455 Sticks

DFS。搜索以棍数为条件循环搜索较好，这样不会超时。

#include <stdio.h>
#include <string.h>
#include <stdlib.h>

#define true  1
#define false 0
#define MAXN  70

int alen;
int parts[MAXN];
char visit[MAXN];
int n, m;

int dfs(int beg, int cnt, int len) {
    int i;

    if (len == 0) {
        ++cnt;
        if (cnt+1 == m)
            return true;

        for (i=0; i<n; ++i)
            if ( !visit[i] )
                break;

        visit[i] = 1;
        if ( dfs(i+1, cnt, alen-parts[i]) )
            return true;
        visit[i] = 0;

        return false;
    }

    for (i=beg; i<n; ++i) {
        if (visit[i] || parts[i]>len)
            continue;
        if (i && parts[i]==parts[i-1] && !visit[i-1])
            continue;
        visit[i] = 1;
        if ( dfs(i+1, cnt, len-parts[i]) )
            return true;
        visit[i] = 0;
    }

    return false;
}

int comp(const void *a, const void *b) {
    return *(int *)b - *(int *)a;
}

int main() {
    int sum;
    int i;

    while (scanf("%d", &n)!=EOF && n) {
        sum = 0;
        for (i=0; i<n; ++i) {
            scanf("%d", &parts[i]);
            sum += parts[i];
        }
        qsort(parts, n, sizeof(int), comp);
        m = n+1;
        while (m > 1) {
            --m;
            if (sum%m)
                continue;
            alen = sum/m;
            if (parts[0] > alen)
                continue;
            memset(visit, 0, sizeof(visit));
            if ( dfs(0, 0, alen) )
                break;
        }
        printf("%d
", alen);
    }

    return 0;
}