【HDOJ】1518 Square

DFS+剪枝。与HDOJ 1455如出一辙。

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

#define MAXN 25

int nums[MAXN], n, len, cnt;
char visit[MAXN];

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

int dfs(int cnt, int beg, int l) {
    int i, flg = 0;
    if (cnt == 3)
        return 1;
    if (l == 0) {
        for (i=0; i<n; ++i) {
            if ( !visit[i] ) {
                visit[i] = 1;
                flg = dfs(cnt+1, i+1, len-nums[i]);
                visit[i] = 0;
                break;
            }
        }
        return flg;
    }

    for (i=beg; i<n; ++i) {
        if ( !visit[i] ) {
            if (i && !visit[i-1] && nums[i] == nums[i-1])
                continue;
            if (nums[i] <= l) {
                visit[i] = 1;
                flg = dfs(cnt, i+1, l-nums[i]);
                visit[i] = 0;
                if (flg) return 1;
            }
        }
    }

    return 0;
}

int main() {
    int case_n, sum;
    int i, j;

    scanf("%d", &case_n);

    while (case_n--) {
        scanf("%d", &n);
        sum = 0;
        for (i=0; i<n; ++i) {
            scanf("%d", &nums[i]);
            sum += nums[i];
        }
        if ( sum&3 )
            printf("no
");
        else {
            len = sum>>2;
            qsort(nums, n, sizeof(int), comp);
            memset(visit, 0, sizeof(visit));
            j = 1;
            for (i=0; i<n; ++i)
                if (nums[i] > len) {
                    j = 0;
                    break;
                }
            if (!j)
                printf("no
");
            else if ( dfs(0, 0, len) )
                printf("yes
");
            else
                printf("no
");
        }
    }

    return 0;
}