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剑指offer之判断链表是否包含环

2019-10-21 18:06 1866 查看

1 问题

判断链表是否包含环

2 思路

2个指针，一个指针走一步，一个指针走2步，如果相遇则有，反之无。

3 代码实现

#include <stdio.h>
#include <stdlib.h>
#define true 1
#define false 0;
typedef struct node
{
int value;
struct node *next;
}Node;
/*
*判断链表是否有环
*/
int isCircleList(Node *head)
{
if (head == NULL)
{
return false;
}
Node *first = NULL;
Node *second = NULL;
first = head;
second = head;
while (second != NULL && (second->next) != NULL && (second->next->next != NULL))
{
first = first->next;
second = second->next->next;
if (first == second)
{
return true;
}
}
return false;
}
int main()
{
Node *head = NULL;
Node *node1 = NULL;
Node *node2 = NULL;
Node *node3 = NULL;
Node *node4 = NULL;
Node *node5 = NULL;
Node *node6 = NULL;
Node *node7 = NULL;
head = (Node *)malloc(sizeof(Node));
node1 = (Node *)malloc(sizeof(Node));
node2 = (Node *)malloc(sizeof(Node));
node3 = (Node *)malloc(sizeof(Node));
node4 = (Node *)malloc(sizeof(Node));
node5 = (Node *)malloc(sizeof(Node));
node6 = (Node *)malloc(sizeof(Node));
node7 = (Node *)malloc(sizeof(Node));
if (head == NULL || node1 == NULL || node2 == NULL || node3 == NULL
|| node4 == NULL || node5 == NULL || node6 == NULL || node7 == NULL)
{
printf("malloc fail\n");
return false;
}
//       node7<-node6 <-node5
//       |       |
//head->node1->node2->node3->node4
head->value = 0;
head->next = node1;
node1->value = 1;
node1->next = node2;
node2->value = 2;
node2->next = node3;
node3->value = 3;
node3->next = node4;
node4->value = 4;
node4->next = node5;
node5->value = 5;
node5->next = node6;
node6->value = 6;
node6->next = node7;
node7->value = 7;
node7->next = node2;
int result = isCircleList(head);
if (result)
{
printf("list have circle\n");
}
else
{
printf("list do not have circle\n");
}
return true;
}

4 运行结果

list have circle

总结

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