nyoj 927 The partial sum problem（dfs）

描述

One day,Tom’s girlfriend give him an array A which contains N integers and asked him:Can you choose some integers from the N integers and the sum of them is equal to K.
 

输入

There are multiple test cases.
Each test case contains three lines.The first line is an integer N(≤N≤),represents the array contains N integers. The second line contains N integers,the ith integer represents A[i](-^≤A[i]≤^).The third line contains an integer K(-^≤K≤^).

输出

If Tom can choose some integers from the array and their them is K,printf ”Of course,I can!”; other printf ”Sorry,I can’t!”.

样例输入

样例输出

Of course,I can!
Sorry,I can't!

两种方法：

第一种直接回溯dfs

 #pragma comment(linker, "/STACK:1024000000,1024000000")
 #include<iostream>
 #include<cstdio>
 #include<cstring>
 #include<cmath>
 #include<math.h>
 #include<algorithm>
 #include<queue>
 #include<set>
 #include<bitset>
 #include<map>
 #include<vector>
 #include<stdlib.h>
 #include <stack>
 using namespace std;
 #define PI acos(-1.0)
 #define max(a,b) (a) > (b) ? (a) : (b)
 #define min(a,b) (a) < (b) ? (a) : (b)
 #define ll long long
 #define eps 1e-10
 #define MOD 1000000007
 #define N 26
 #define inf 1e12
 int n,m,flag;
 int a[N];
 int vis[N];
 void dfs(int now,int num){
    if(num>=m){
          if(num==m){
             flag=;
          }
          return;
    }
    for(int i=now;i<n;i++){
       if(!vis[i]){
          vis[i]=;
          dfs(i+,num+a[i]);
          if(flag){
             return;
          }
          vis[i]=;
       }
    }
 }
 int main()
 {
    while(scanf("%d",&n)==){
       for(int i=;i<n;i++){
          scanf("%d",&a[i]);
       }
       scanf("%d",&m);
       memset(vis,,sizeof(vis));
       flag=;
       dfs(,);
       if(flag){
          printf("Of course,I can!\n");
       }else{
          printf("Sorry,I can't!\n");
       }
    }
     return ;
 }

第二种类似01背包思想的dfs

 #pragma comment(linker, "/STACK:1024000000,1024000000")
 #include<iostream>
 #include<cstdio>
 #include<cstring>
 #include<cmath>
 #include<math.h>
 #include<algorithm>
 #include<queue>
 #include<set>
 #include<bitset>
 #include<map>
 #include<vector>
 #include<stdlib.h>
 #include <stack>
 using namespace std;
 #define PI acos(-1.0)
 #define max(a,b) (a) > (b) ? (a) : (b)
 #define min(a,b) (a) < (b) ? (a) : (b)
 #define ll long long
 #define eps 1e-10
 #define MOD 1000000007
 #define N 26
 #define inf 1e12
 int n,m;
 int a[N];
 bool dfs(int cur,int num){
    if(num>=m){
       if(num==m){
          return true;
       }
       return false;
    }
    if(cur>=n) return false;
    if(dfs(cur+,num+a[cur])) return true;
    return dfs(cur+,num);

 }
 int main()
 {
    while(scanf("%d",&n)==){
       for(int i=;i<n;i++){
          scanf("%d",&a[i]);
       }
       scanf("%d",&m);
       if(dfs(,)){
          printf("Of course,I can!\n");
       }else{
          printf("Sorry,I can't!\n");
       }
    }
     return ;
 }