HDU-1427-速算24点

HDU-1427-速算24点

http://acm.hdu.edu.cn/showproblem.php?pid=1427

4个数通过 +，—，*，/和加括号，计算得24,

枚举数字和运算符，DFS即可，注意题目要求计算过程中都不能出现小数，所以做除法时稍作处理

枚举数组可用algorithm里的next_permutation

The next_permutation() function attempts to transform the given range of elements [start,end) into the next lexicographically greater permutation of elements. If it succeeds, it returns true, otherwise, it returns false. 

#include<iostream>
#include<cstdio>
#include<cstring>
#include<cstdlib>
#include<algorithm>
using namespace std;
int flag;
int num[4];
int cmp(const void *a,const void *b)
{
	return *(int *)a-*(int *)b;
}
void dfs(int sum,int cur,int m)
{
	if(flag)
	return;
	if(m==3)
	{
		if(sum+cur==24||sum-cur==24||sum*cur==24)
		flag=1;
		if(cur!=0&&sum%cur==0&&sum/cur==24)
		flag=1;
		return;
	}
	dfs(sum+cur,num[m+1],m+1);  //先计算前一部分
	dfs(sum-cur,num[m+1],m+1);
	dfs(sum*cur,num[m+1],m+1);
	if(cur!=0&&sum%cur==0)
	dfs(sum/cur,num[m+1],m+1);
	dfs(sum,cur+num[m+1],m+1);  //先计算后一部分，相当于加括号
	dfs(sum,cur-num[m+1],m+1);
    dfs(sum,cur*num[m+1],m+1);
	if(num[m+1]!=0&&cur%num[m+1]==0)
	dfs(sum,cur/num[m+1],m+1);
}
int main()
{
	int i;
	char str[5];
	while(scanf("%s",str)!=EOF)
	{
		if(strlen(str)==2)
		num[0]=10;
		else
		{
			if(str[0]=='A')
			num[0]=1;
			else if(str[0]=='J')
			num[0]=11;
			else if(str[0]=='Q')
			num[0]=12;
			else if(str[0]=='K')
			num[0]=13;
			else
			num[0]=str[0]-'0';
		}
		for(i=1;i<=3;i++)
		{
			scanf("%s",str);
			if(strlen(str)==2)
		    num[i]=10;
		    else
			{
			   if(str[0]=='A')
			   num[i]=1;
			   else if(str[0]=='J')
			   num[i]=11;
			   else if(str[0]=='Q')
			   num[i]=12;
		       else if(str[0]=='K')
		       num[i]=13;
			   else
			   num[i]=str[0]-'0';
			}
		}
		qsort(num,4,sizeof(num[0]),cmp);
		flag=0;
		do
		{
			dfs(num[0],num[1],1);
		}while(next_permutation(num,num+4)&&!flag);
		if(flag)
		printf("Yes\n");
		else
		printf("No\n");
	}
	return 0;
}