算法题（使用Map查找链表中的循环长度） _Map查找链表中的循环长度

本文概述

C ++
Java

编写一个程序, 检查给定的链表是否包含循环, 如果存在循环, 则返回循环中的节点数。例如, 在下面链接的列表中存在一个循环, 并且循环的长度为4。如果不存在该循环, 则该函数应返回0。

文章图片
方法：在这篇文章中, 我们将使用Map存储存在的节点的地址链表作为键, 其位置作为值。
以下是分步方法：

遍历链表的每个节点, 并保持位置从一个开始。在每个节点之后增加位置。
检查Map中是否存在该节点。
如果Map不包含该节点的地址, 则将其及其位置插入Map。
如果Map已经包含该节点的地址, 则返回其位置之间的差。
如果找不到这样的节点, 则返回0。

下面是上述方法的实现：
C ++

//C++ program to find length of loop //in a linked list using Map #include < bits/stdc++.h> using namespace std; //Linked List node struct Node { int data; struct Node* next; Node( int num) { data = https://www.lsbin.com/num; next = NULL; } }; //Function detects and counts loop //nodes in the list. If loop is not there, //then returns 0 int countNodesinLoop( struct Node* head) { struct Node* p = head; int pos = 0; //Maintain a map to store addresses //of node and their position unordered_map< Node*, int> m; //Traverse through the linked list while (p != NULL) { //If the node is not present in the map if (m.find(p) == m.end()) { m = pos; pos++; } //if the node is present else { //Return difference between //position of the present node and //position where that node occured before return (pos - m 【算法题（使用Map查找链表中的循环长度）】); } p = p-> next; } //Return 0 to indicate //there is no loop return 0; } //Driver code int main() { //Create nodes of the linked list struct Node* head = new Node(1); head-> next = new Node(2); head-> next-> next = new Node(3); head-> next-> next-> next = new Node(4); head-> next-> next-> next-> next = new Node(5); //Create a loop for testing the function head-> next-> next-> next-> next-> next = head-> next; //Call the function for the above linked list cout < < countNodesinLoop(head) < < endl; return 0; }

Java

//Java program to find length of loop //in a linked list using Map import java.util.*; import java.io.*; class GFG{static class Node { int data; Node next; //Constructor Node( int num) { data = https://www.lsbin.com/num; next = null ; } }//Function detects and counts loop //nodes in the list. If loop is not there, //then returns 0 public static int countNodesinLoop(Node head) { Node p = head; int pos = 0 ; //Maintain a map to store addresses //of node and their position HashMap< Node, Integer> m = new HashMap< Node, Integer> (); //Traverse through the linked list while (p != null ) {//If the node is not present in the map if (!m.containsKey(p)) { m.put(p, pos); pos++; } //If the node is present else {//Return difference between //position of the present //node and position where //that node occured before return (pos - m.get(p)); } p = p.next; } //Return 0 to indicate //there is no loop return 0 ; } //Driver code public static void main (String[] args) {//Create nodes of the linked list Node head = new Node( 1 ); head.next = new Node( 2 ); head.next.next = new Node( 3 ); head.next.next.next = new Node( 4 ); head.next.next.next.next = new Node( 5 ); //Create a loop for testing the function head.next.next.next.next.next = head.next; //Call the function for the above linked list System.out.println(countNodesinLoop(head)); } } //This code is contributed by adityapande88

输出如下