计算其中有多少 "element" 出现在双向链表中

Question

我的 nbSandwichs(int type) 方法有问题它应该通过双向链表并计算相同类型的三明治出现的次数，一切都很好，除了最后一个打印 0 的三明治，这是我不明白的，我的检查方法是这样说的它不存在，但是当我创建一个 get last 方法时，它确实存在。我的 nbSandwichs 方法缺少什么条件？我的 while 循环实际上没有到达最后一个节点吗？

谢谢

main class : 
    Sandwich s1 = new Sandwich(1);
        Sandwich s1 = new Sandwich(1);
        Sandwich s2 = new Sandwich(15);
        Sandwich s3 = new Sandwich(15);
        Sandwich s4 = new Sandwich(4);
        Sandwich s5 = new Sandwich(15);

        APreparer a1 = new APreparer();
        a1.addfirst(s1); 
        a1.addfirst(s2);
        a1.addfirst(s3);
        a1.addfirst(s4);
        a1.addfirst(s5);

        System.out.println(a1.nbSandwichs(15)); // PRINTS : 3 OK 
        System.out.println(a1.nbSandwichs(1)); // PRINTS : 0 NOT OK 


    public class Sandwich {

        private int type;

        public Sandwich(int type) {
            this.type = type;
            commandes[type]++;
        }

    public class APreparer {

        private UneCommande first;
        private UneCommande last;

        public void addfirst(Sandwich sandwich) {
            UneCommande nouvelle = new UneCommande(sandwich);
            if (first == null) {
                first = nouvelle;
                last = nouvelle;

            } else {
                first = first.addFirst(sandwich);
            }
        }

    int nbSandwichs(int type) {
        if (first == null) {
            return 0;
        } else {
            return first.nbSandwichs(type);
        }
    }

    }


    public class UneCommande {

        private Sandwich sandwich;
        private UneCommande next;
        private UneCommande previous;

        public UneCommande(Sandwich sandwich) {
            this.sandwich = sandwich;
        }

        public UneCommande addFirst(Sandwich sandwich) {
            UneCommande current = this;
            UneCommande newSand = new UneCommande(sandwich);
            newSand.next = current;
            this.previous = newSand;

            return newSand;
        }
int nbSandwichs(int type) {
        int counter = 0;
        UneCommande current = this;

        if (!(check(type))) {
            return 0;
        } else {
            while (current.next != null) {
                if (current.sandwich.getType() == type) {
                    counter++;
                }
                current = current.next;
            }
        }
        return counter;
    }

    boolean check(int type) {
        UneCommande current = this;
        while (current != null) {
            if (current.sandwich.getType() == type) {
                System.out.println("EXIST");
                return true;
            }
            current = current.next;
        }

        return false;
    }
}

Answer 1

您的循环计算节点的长度为 current.next != null。当 current 是列表中的最后一个节点时，current.next 将是 null，因此不计算在内。

计算其中有多少 "element" 出现在双向链表中

Counting how many of that "element" appear in a doubly linked list

java

doubly-linked-list

find-occurrences