24点游戏算法

描述	问题描述：给出4个1-10的数字，通过加减乘除，得到数字为24就算胜利 输入： 4个1-10的数字。[数字允许重复，测试用例保证无异常数字] 输出： true or false
知识点	循环
运行时间限制	10M
内存限制	128
输入	输入4个int整数
输出	返回能否得到24点，能输出true，不能输出false
样例输入	7 2 1 10
样例输出	true

package com.oj5;

import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;

public class Oj {
	private static int calculate(int[] operator,int[] data){
		int[] op = new int[3];
		int[] da = new int[4];
		int oppos = 0,dapos = 0;
		int posop = 0,posda = 0;
		da[dapos++] = data[posda++];
		for(int i = 0;i <= 2; i++)
			if(operator[i]==1||operator[i]==2){
				da[dapos++] = data[posda++];
				op[oppos++] = operator[i];
				//System.out.println("add");
			}else if(operator[i]==3||operator[i]==4){
				int left = da[--dapos];
				int right = data[posda++];
				int result;
				if(operator[i]==3)
					result = left*right;
				else
					result = left/right;
				da[dapos++] = result;
				//System.out.println(result);
			}
		int begin = 0;
		int result = da[begin++];
		//System.out.println("oppos: "+oppos);
//		if(oppos==1)
//			System.out.println(op[0]);
		for(int i = 0;i < oppos; i++)
			if(op[i]==1){
				//System.out.println(result+" ++");
				result += da[begin++];
				//System.out.println(result);
			}else if(op[i]==2){
				//System.out.println(result+" --");
				result -= da[begin++];
				//System.out.println(result);
			}
		//System.out.println(op[0]);
		return result;
//		if(result==24)
//			return true;
//		else
//			return false;
	}
	static List<Integer> list = new ArrayList<Integer>();
	private static void expression(int[] operator,int pos,int num,int[] data){
		if(pos==num){
			list.add(calculate(operator,data));
			return ;
		}
		
		operator[pos] = 1;
		expression(operator,pos+1,num,data);
		operator[pos] = 2;
		expression(operator,pos+1,num,data);
		operator[pos] = 3;
		expression(operator,pos+1,num,data);
		operator[pos] = 4;
		expression(operator,pos+1,num,data);
	}
	
	public static void main(String[] args) {
		Scanner in = new Scanner(System.in);
		int[] data = new int[4];
		int[] operator = new int[3];
		for(int i = 0;i < 4; i++)
			data[i] = in.nextInt();
		
		expression(operator,0,3,data);
		for(int i = 0;i < list.size(); i++)
			if(list.get(i)==24){
				System.out.println("true");
				return ;
			}
		System.out.println("false");
	}
}