AcWing 167 木棒 (搜索 + 剪枝)

https://www.acwing.com/problem/content/description/169/

剪枝剪枝还是剪枝

#include<cstdio>
#include<cstring>
#include<algorithm>
#include<iostream>
#include<cmath>
#include<stack>
#include<queue>
using namespace std;
typedef long long ll;

const int maxn = 100;

int n, len;
int a[maxn], used[maxn];

bool dfs(int d, int now, int num, int goal){
	if(d == len / goal){
		return true;
	}
	
	if(now == goal) return dfs(d + 1, 0, 0, goal);
	
	int fail = 0;
	for(int i = num + 1; i <= n; ++i){
		if(used[i] || now + a[i] > goal || fail == a[i]) continue;
		
		used[i] = 1;
		if(dfs(d, now + a[i], i, goal)) return true;
		fail = a[i];
		used[i] = 0;
		if(!now || now + a[i] == goal) return false;
	}
	return false;
}

bool cmp(int x, int y){
	return x > y;
}

ll read(){ ll s=0,f=1; char ch=getchar(); while(ch<'0' || ch>'9'){ if(ch=='-') f=-1; ch=getchar(); } while(ch>='0' && ch<='9'){ s=s*10+ch-'0'; ch=getchar(); } return s*f; }

int main(){
	while(1){
		len = 0;
		n = read();
		if(!n) break;
		
		for(int i=1;i<=n;++i) a[i] = read(), len += a[i];
		
		sort(a + 1, a + 1 + n, cmp);
		
		for(int i=a[1]; i<=len; ++i){
			if(len % i == 0){
				memset(used, 0, sizeof(used));
				if(dfs(0, 0, 0, i)){
					printf("%d\n",i);
					break;
				}
			}
		}
	}
	return 0;
}