求指教

[leader_tk]

Java用递归编写的 一个射击运动员打靶，靶一共有 10 环，连开 6 枪打中 45 环的可能性有多少种?

[nayi_224]

import java.util.Arrays;

public class Test56 {
	static int nn = 0;
	public static void main(String[] args) {
		aa(0, 0, new int[6]);
		System.out.println(nn);
	}
	public static void aa(int total, int num, int[] arr){
		if(num <= 6 && total == 45){
			nn++;
			System.out.println(Arrays.toString(arr));
			return;
		}
		
		if(num >= 6 || total > 45)
			return;
		
		int i = 11;
		while(i-- > 0){
			int[] temp = new int[6];
			System.arraycopy(arr, 0, temp, 0, 6);
			temp[num] = i;
			aa(total + i, num + 1, temp);
		}
	}
}

[汉森cd]

这种问题用数学方法解决了直接print了，如果非要用递归，如下：
class Test {
private int mGoalScores = 45;
private int mRoundNum = 6;
private int mMinScore = 0;
private int mMaxScore = 10;
private int[] mScoresArr;
private int mMethodNum = 0;

public Test(){
mScoresArr = new int[mRoundNum];
}

private boolean checkSum() {
int sum = 0;
for (int ii=0; ii<mRoundNum; ii++) {
sum += mScoresArr[ii];
}

return sum==45;
}

private void printArr() {
for (int ii=0; ii<mRoundNum; ii++) {
System.out.print(mScoresArr[ii] + " ");
}

System.out.println("");
}

private void getRoundScore(int round) {
if (mRoundNum == round) {
if (true == checkSum()) {
printArr();
mMethodNum++;
}
return;
}

for (int ii=mMinScore; ii<=mMaxScore; ii++) {
mScoresArr[round] = ii;
getRoundScore(round+1);
}
}

public void startCal() {
getRoundScore(0);
System.out.println("Possible cases: " + mMethodNum);
}
}
总结果有14748可能。
给分。

[汉森cd]

优化版

class Test {
    private int mGoalScores = 45;   // 目标值
    private int mRoundNum = 6;      // 轮数
    private int mMinScore = 0;      // 最低得分
    private int mMaxScore = 10;     // 最高得分
    private int[] mScoresArr;       // 得分记录
    private int mMethodNum = 0;     // 可能得到目标值的情况数
    private int mSum = 0;           // 某一轮的分数总和
    
    public Test(){
        mScoresArr = new int[mRoundNum];
    }
    
    private boolean continueNextRound(int round) {
        if (mRoundNum == round) {
            if (mGoalScores == mSum) {
                for (int ii=0; ii<mRoundNum; ii++) {
                    System.out.print(mScoresArr[ii] + " ");
                }
                System.out.println("");

                mMethodNum++;
            }
            return false;
        }
        
        return true;
    }
    
    private void getRoundScore(int round) {
        if (false == continueNextRound(round)) {
            return;
        }
        
        for (int ii=mMinScore; ii<=mMaxScore; ii++) {
            mScoresArr[round] = ii;
            mSum += mScoresArr[round];
            getRoundScore(round+1);
            mSum -= mScoresArr[round];
        }
    }
    
    public void startCal() {
        getRoundScore(0);
        System.out.println("Possible cases: " + mMethodNum);
    }
}

引用 2 楼 rabbit0404 的回复:

这种问题用数学方法解决了直接print了，如果非要用递归，如下：
class Test {
private int mGoalScores = 45;
private int mRoundNum = 6;
private int mMinScore = 0;
private int mMaxScore = 10;
private int[] mScoresArr;
private int mMethodNum = 0;

public Test(){
mScoresArr = new int[mRoundNum];
}

private boolean checkSum() {
int sum = 0;
for (int ii=0; ii<mRoundNum; ii++) {
sum += mScoresArr[ii];
}

return sum==45;
}

private void printArr() {
for (int ii=0; ii<mRoundNum; ii++) {
System.out.print(mScoresArr[ii] + " ");
}

System.out.println("");
}

private void getRoundScore(int round) {
if (mRoundNum == round) {
if (true == checkSum()) {
printArr();
mMethodNum++;
}
return;
}

for (int ii=mMinScore; ii<=mMaxScore; ii++) {
mScoresArr[round] = ii;
getRoundScore(round+1);
}
}

public void startCal() {
getRoundScore(0);
System.out.println("Possible cases: " + mMethodNum);
}
}
总结果有14748可能。
给分。

[qq_39936465]

public class test{

static int count=0;

public static void main (String[] args){
sum(0,6);
System.out.println("count="+count);
}
public static void sum(int x,int round){
int s=x;//保存上轮数字
if (y>0){ //判断轮次没有耗尽
for (int i=0;i<11；i++) { //每轮可能得分0-11
x = s + i; //到本轮为止得分
if(x==45){
count++;
sum(x,y-1); 下轮零环的可能性
}else {
if(x<45){
sum(x,y-1); //分数不足开始下轮射击
}else
continue; //分数超过的话跳过
}
}
}
}
}

[qq_39936465]

递归 基本就是自身调用自身形成 循环嵌套，先看清变化量 ，把循环相同部分提取出来，然后对自身进行变量传递。

本题 每轮可能得分是固定的，变化的是到上轮为止的总得分和轮次。

[qq_39936465]

抱歉刚刚有部分代码写错了，下面是修正版

public class test{

static int count=0;

public static void main (String[] args){
sum(0,6);
System.out.println("count="+count);
}
public static void sum(int x,int round){
int s=x;
if (round>0){
for (int i=0;i<11;i++) {
x = s + i;
if(x==45){
count++;

}else {
if(x<45){
sum(x,round-1);
}else
continue;
}
}
}
}
}

count= 14748

[leader_tk]

请问一下做这种题的思想

[verejava]

数据结构算法 之 递归算法 http://www.verejava.com/?id=173208157961122

[CivKeeper]

class OutPut{
	private int sum = 0;
	
	public void SetSum() {
		sum++;
	}
	
	public int OutSum() {
		return sum;
	}
}

// 设计计算方法
class Calculate extends OutPut{
	public void ComPut(int score,int num) {
		if (score < 0 || score > (num + 1) * 10) 
			return;
		
		if (num == 0) {
			SetSum();
			return;
		}
		
		for (int i = 0;i <= 10;++i)
			ComPut(score-i,num-1);
	}
}

public class SheBar {
	public static void main(String[] args) {
		
		Calculate a = new Calculate();
		
		a.ComPut(45, 5);
		
		System.out.println(a.OutSum());
	}
}