问题描述

有100人围成一圈，顺序排号。从第1个人开始报数（从1到3报数），凡报到3的人退出圈子，问最后留下的是原来的第几号的那位。
代码实现：

public class Count3Quit1 {
    //利用数组
    public static void main(String[] args) {
        boolean[] arr = new boolean[100];

        for(int i=0; i<arr.length; i++) {
            arr[i] = true;
        }
        
        int leftCount = arr.length;
        int countNum = 0;
        int index = 0;
        
        while(leftCount > 1) {
            if(arr[index] == true) {
                countNum ++;
                if(countNum == 3) {
                    countNum = 0;
                    arr[index] = false;
                    leftCount --;
                }
            }
            
            index ++;
            
            if(index == arr.length) {
                index = 0;
            }
        }
        
        for(int i=0; i<arr.length; i++) {
            if(arr[i] == true) {
                System.out.println(i+1);
            }
        }
    }
}

面向对象风格的实现：

public class Count3Quit2 {

    public static void main(String[] args) {
        KidCircle kc = new KidCircle(100);
        int deleteCount = 0;
        Kid kid = kc.first;

        while (kc.count > 1) {
            deleteCount++;
            if (deleteCount == 3) {
                deleteCount = 0;
                kc.delete(kid);
            }

            kid = kid.right;
        }

        System.out.println(kid.id+1);
    }
}

class Kid {
    int id;
    Kid left, right;
}

class KidCircle {
    Kid first, last;
    int count = 0;

    public KidCircle(int num) {
        for (int i =0; i < num; i++) {
            add();      
        }
    }

    public void add() {
        Kid kid = new Kid();
        kid.id = count;

        if (count < 0) {
            return ;
        } else if (count == 0) {
            kid.left = kid;
            kid.right = kid;
            first = kid;
            last = kid;
        } else {
            first.left = kid;
            last.right = kid;
            kid.left = last;
            kid.right = first;
            last = kid;
        }

        count++;
    }

    public void delete(Kid kid) {
        if (count <= 0) {
            return ;
        } else if (count == 1) {
            first = last = null;
        } else {
            kid.left.right = kid.right;
            kid.right.left = kid.left;
            if (kid == first) {
                first = kid.right;
            }
            if (kid == last) {
                last = kid.left;
            }
        }

        count--;
    }
}