编程之美--1.16 24点游戏

解答

1 这道题目结合知乎的24点会非常有意思。http://zhuanlan.zhihu.com/MathplusPlus/19817404

2 我这里先放枚举法代码。

static double Threshold = 1E-6;
	static int cardsNumber = 4;
	static int resultValue = 24;
	static double[] number;
	static String[] result;
	public static boolean PointGame(int n){
		if(n==1){
			if(Math.abs(number[0]-resultValue)<Threshold){
				return true;
			}
			else{
				return false;
			}
		}
		
		for(int i=0;i<n;i++){
			for(int j=i+1;j<n;j++){
				double a,b;
				String expa,expb;
				a = number[i];
				b = number[j];
				number[j]=number[n-1];
				
				expa = result[i];
				expb = result[j];
				result[j] = result[n-1];
				
				result[i] = "("+expa+"+"+expb+")";
				number[i] = a+b;
				if(PointGame(n-1)){
					return true;
				}
				
				result[i] = "("+expa+"-"+expb+")";
				number[i] = a-b;
				if(PointGame(n-1)){
					return true;
				}
				
				result[i] = "("+expb+"-"+expa+")";
				number[i] = b-a;
				if(PointGame(n-1)){
					return true;
				}
				
				result[i] = "("+expa+"*"+expb+")";
				number[i] = a*b;
				if(PointGame(n-1)){
					return true;
				}
				
				if(b!=0){
					result[i] = "("+expa+"/"+expb+")";
					number[i] = a/b;
					if(PointGame(n-1)){
						return true;
					}
				}
				
				if(a!=0){
					result[i] = "("+expb+"/"+expa+")";
					number[i] = b/a;
					if(PointGame(n-1)){
						return true;
					}
				}
				
				number[i]=a;
				number[j]=b;
				result[i]=expa;
				result[j]=expb;
			}
		}
		return false;
	}