任意4个1-13数字，加减乘除计算24点。
实现原理：
1）排列组合4个数字
2）计算每次排列组合的可能性
Cal24.java
import java.util.HashSet;import java.util.Set; public class Cal24 { private static final double precision = 0.00001; private static final int target = 24; public String[] execute(String[] inputs) { int[] digits = new int[4]; for (int i = 0; i < inputs.length; i++) { digits[i] = Integer.valueOf(inputs[i]); } return new String[]{calc(digits)}; } private String calc(final int data[]){ final Set<String> out = new HashSet<String>(); Combination digit = new Combination() { @Override protected void handle(int[] result) { final int[] r = result; Combination oper = new Combination(){ @Override protected void handle(int[] c) { double x = r[0]; for (int i = 0; i < r.length - 1; i++) { x = doCalculate(x, r[i + 1], c[i]); } if(Math.abs(Math.abs(x) - target) < precision || Math.abs(Math.abs(1/x) - target) < precision){ StringBuilder sb = new StringBuilder(); for (int j = 0; j < r.length; j++) { sb.append(r[j]); if(j != r.length - 1){ sb.append(getOperation(c[j])); } } out.add(sb.toString()); } } }; oper.combine(new int[]{0, 1, 2, 3}, data.length - 1, true); } }; digit.combine(data); StringBuilder sb = new StringBuilder(); for (String string : out) { sb.append(string); sb.append("/n"); } return sb.toString(); } private double doCalculate(double x, double y, int operation){ switch (operation) { case 0: return x + y; case 1: return x - y; case 2: return x * y; case 3: return x / y; default: return 0; } } private static String getOperation(int operation){ switch (operation) { case 0: return "+"; case 1: return "-"; case 2: return "*"; case 3: return "/"; default: return ""; } } public static void main(String[] args) { System.out.println(new Cal24().calc(new int[]{1, 5, 5, 5})); }}Combination.java
public abstract class Combination { private boolean repeat; private int total = 0; public void combine(int data[]){ combine(data, data.length, false); } public void combine(int data[], int count){ combine(data, count, false); } public void combine(int data[], int count, boolean repeat){ this.repeat = repeat; int times = data.length; int size = (int)Math.pow(times, count); for (int i = 0; i < size; i++) { int[] result = toArray(data, i, count); if(result != null){ handle(result); total ++; } } } private int[] toArray(int data[], int i, int count){ int [] indices = new int[count]; int times = data.length; for (int j = 0; j < count; j++) { int temp = 0; if(i > 0){ temp = i%times; i = (i - temp)/times; } indices[j] = temp; } if(!repeat){ //remove repetition for (int x = 0; x < count; x++) { for(int y = 0; y < count; y++){ if(x != y){ if(indices[x] == indices[y]) return null; } } } } int [] result = new int[count]; for (int x = 0; x < count; x++) { int selected = data[indices[x]]; result[x] = selected; } return result; } public int getTotal() { return total; } protected abstract void handle(int[] result);}以上所述就是本文的全部内容了，希望大家能够喜欢。