hdu1258---Sum It Up解题报告（DFS入门）

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                                          Sum It Up题目链接

题目大意：输入一个val,和一个n ，然后n个数，求n个数中相加=val的所有情况

（val不一定要n个数组成）,但一定要是降序相加(即第一个相加数是最大的)

AC Code:

#include<iostream>
#include<sstream>
#include<cstdlib>
#include<cmath>
#include<algorithm>
#include<cstring>
#include<cstdio>
#include<map>
#include<vector>
#include<stack>
#include<queue>
#include<set>
#include<list>
#define mod 998244353
#define INF 0x3f3f3f3f
#define Min 0xc0c0c0c0
#define mst(a) memset(a,0,sizeof(a))
#define f(i,a,b) for(int i = a; i < b; i++)
using namespace std;
typedef long long ll;
const int MAX_N = 1e6 + 5;
int n, val;
int arr[15], num[15];
bool vis[15];
bool flag;
void dfs(int sum, int s){
    if(sum == val){
        for(int j = 1; j < s - 1; j++){
            cout<<num[j]<<"+";
        }
        cout<<num[s - 1]<<endl;
        flag = true;
        return ;
    }
    for(int i = 1; i <= n; i++){
        if(sum + arr[i] <= val && num[s - 1] >= arr[i] && !vis[i]){
            num[s] = arr[i];
            vis[i] = 1;
            dfs(sum + arr[i], s + 1);
            vis[i] = 0;
            while(arr[i] == arr[i + 1] && i <= n) i++;
        }
    }
}
int main(){
    //freopen("c1.txt", "w", stdin);
    //freopen("c2.txt", "r", stdout);
    ios::sync_with_stdio(false);
    while(cin>>val>>n){
        if(val == 0 && n == 0){
            break;
        }
        mst(num), mst(vis);
        for(int i = 1; i <= n; i++){
            cin>>arr[i];
            //cin>>arr[i];
        }
        flag = false;
        num[0] = INF;
        cout<<"Sums of "<<val<<":"<<endl;
        dfs(0, 1);
        if(!flag){
           cout<<"NONE"<<endl;
        }
    }
    //fclose(stdin);
    //fclose(stdout);
    return 0;
}