Java语言怎么实现扑克牌4张用加减乘除，程序自动产生算式计算的实现的过程是什么

Question

Java语言怎么实现扑克牌4张用加减乘除，使得得到的算式的结果是24，程序自动产生算式计算的实现的过程是什么

Answer 1

使用递归方式生成所有可能的表达式，并计算其结果
代码如下

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

public class Poker24Game {

    private static final double TARGET = 24.0;
    private static final double EPSILON = 1e-6;

    public static void main(String[] args) {
        int[] nums = {1, 2, 3, 4}; // 扑克牌的数字值

        List<String> expressions = findExpressions(nums);
        for (String expression : expressions) {
            System.out.println(expression + " = " + TARGET);
        }
    }

    public static List<String> findExpressions(int[] nums) {
        List<String> expressions = new ArrayList<>();
        helper(nums, new double[nums.length], 0, expressions);
        return expressions;
    }

    private static void helper(int[] nums, double[] results, int count, List<String> expressions) {
        if (count == nums.length) {
            if (Math.abs(results[0] - TARGET) < EPSILON) {
                String expression = buildExpression(results, nums);
                expressions.add(expression);
            }
            return;
        }

        for (int i = 0; i < nums.length; i++) {
            if (nums[i] == Integer.MAX_VALUE) {
                continue;
            }
            int num = nums[i];
            nums[i] = Integer.MAX_VALUE;

            results[count] = num;
            helper(nums, results, count + 1, expressions);

            results[count] = -num;
            helper(nums, results, count + 1, expressions);

            results[count] = num;
            for (int j = i + 1; j < nums.length; j++) {
                if (nums[j] == Integer.MAX_VALUE) {
                    continue;
                }
                int nextNum = nums[j];
                nums[j] = Integer.MAX_VALUE;

                results[count] = num + nextNum;
                helper(nums, results, count + 1, expressions);

                results[count] = num - nextNum;
                helper(nums, results, count + 1, expressions);

                results[count] = num * nextNum;
                helper(nums, results, count + 1, expressions);

                if (nextNum != 0) {
                    results[count] = num / nextNum;
                    helper(nums, results, count + 1, expressions);
                }

                if (num != 0) {
                    results[count] = nextNum / num;
                    helper(nums, results, count + 1, expressions);
                }

                nums[j] = nextNum;
            }

            nums[i] = num;
        }
    }

    private static String buildExpression(double[] results, int[] nums) {
        StringBuilder sb = new StringBuilder();
        for (int i = 0; i < results.length; i++) {
            if (i > 0) {
                if (results[i] >= 0) {
                    sb.append(" + ");
                } else {
                    sb.append(" - ");
                }
            }
            sb.append(Math.abs(results[i]));
        }
        for (int num : nums) {
            sb.append(" = ").append(num);
        }
        return sb.toString();
    }
}