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
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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}));
}
}
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Combination.java
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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);
}
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