【HDOJ】1258 Sum It Up

典型的深搜，剪枝的时候需要跳过曾经搜索过的相同的数目，既满足nums[i]=nums[i-1]&&visit[i-1]==0，visit[i-1]==0可以说明该点已经测试过。

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

#define MAXNUM 1005

int nums[MAXNUM];
int visit[MAXNUM];
int t, n;

void output() {
    int i, j=0;

    for (i=0; i<t; ++i) {
        if (j && visit[i])
            printf("+%d", nums[i]);
        if (j==0 && visit[i]) {
            printf("%d", nums[i]);
            j = 1;
        }
    }
    printf("
");
}

int check(int index, int sum) {
    if (index<0 || index>=t || visit[index] || sum+nums[index]>n)
        return 0;
    return 1;
}

int dfs(int beg, int sum) {
    int i, val=0;

    if (sum == n) {
        output();
        return 1;
    }

    for (i=beg; i<t; ++i) {
        if (i>beg && nums[i]==nums[i-1] && visit[i-1]==0)
            continue;
        if (check(i, sum)) {
            visit[i] = 1;
            if (dfs(i+1, sum+nums[i]))
                val = 1;
            visit[i] = 0;
        }
    }

    return val;
}

int main() {
    int i;

    while (scanf("%d%d", &n, &t)!=EOF && (n||t)) {
        for (i=0; i<t; ++i)
            scanf("%d", &nums[i]);
        memset(visit, 0, sizeof(visit));
        printf("Sums of %d:
", n);
        if ( !dfs(0, 0) )
            printf("NONE
");
    }
    return 0;
}