CSU 1600 Twenty-four point

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1600: Twenty-four point

Time Limit: 1 Sec   Memory Limit: 128 MB
Submit: 530   Solved: 86
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Description

Given four numbers, can you get twenty-four through the addition, subtraction, multiplication, and division? Each number can be used only once.

Input

The input consists of multiple test cases. Each test case contains 4 integers A, B, C, D in a single line (1 <= A, B, C, D <= 13).

Output

For each case, print the “Yes” or “No”. If twenty-four point can be get, print “Yes”, otherwise, print “No”.

Sample Input

2 2 3 9
1 1 1 1 
5 5 5 1

Sample Output

Yes
No
Yes

HINT

For the first sample, (2/3+2)*9=24.

Source

今天碰巧看到《编程之美》这本书上对这道题有详细的讲解。

拿来练习练习。

#include <stdio.h>
#include <math.h>
const int MAXN=4;
double nums[MAXN];
bool isSolve=false;
void dfs(int n)
{
        if(isSolve)
                return;
        if(n==1&&fabs(nums[0]-24)<=1e-10)
        {
                isSolve=true;
                return;
        }
        for(int i=0;i<n;i++)
        {
                for(int j=i+1;j<n;j++)
                {
                        double a=nums[i];
                        double b=nums[j];
                        nums[j]=nums[n-1];
                        nums[i]=a+b;
                        dfs(n-1);
                        nums[i]=a-b;
                        dfs(n-1);
                        nums[i]=b-a;
                        dfs(n-1);
                        nums[i]=a*b;
                        dfs(n-1);
                        if(a!=0)
                        {
                                nums[i]=b/a;
                                dfs(n-1);
                        }
                        if(b!=0)
                        {
                                nums[i]=a/b;
                                dfs(n-1);
                        }
                        nums[i]=a;
                        nums[j]=b;
                }
        }
}
 
int main()
{
        while(scanf("%lf%lf%lf%lf",&nums[0],&nums[1],&nums[2],&nums[3])>0)
        {
                isSolve=false;
                dfs(4);
                if(isSolve)
                        printf("Yes\n");
                else
                        printf("No\n");
        }
        return 0;
}
 
/**************************************************************
    Problem: 1600
    User: 0905130123
    Language: C++
    Result: Accepted
    Time:156 ms
    Memory:964 kb
****************************************************************/