【轻知识】反转链表、快慢指针检查环

惭愧，翻开旧博客，三年多前看郝斌视频，写过一次链表（那个视频倒是没讲反转链表）。现在，好好学算法把。少年。

#include<stdio.h>
#include<stdlib.h>

typedef struct Node {
    int data;
    struct Node* pNext;
} NODE,*PNODE;

PNODE create_list();
void traverse_list(PNODE);
PNODE reverse_list(PNODE);
int check_circle(PNODE pHead);
PNODE create_circle_list();
int main() {
    PNODE pHead = create_list();
    traverse_list(pHead);
    pHead = reverse_list(pHead);
    printf("--------\n");
    printf("%d", pHead->pNext->data);
    printf("%d", pHead->pNext->pNext->data);
    traverse_list(pHead);
    PNODE circle_list= create_circle_list();
    int is_circle = check_circle(circle_list);
    printf("is_circle=%d\n", is_circle);
}
PNODE create_list() {
    //1.首先mallc 一个地址
    PNODE pHead = (PNODE)malloc(sizeof(NODE));
    if (pHead == NULL) {
        printf("malloc error");
    }
    int len;
    printf("please input len:");
    scanf("%d", &len);
    printf("len=%d\n", len);
    PNODE tempNode = pHead;
    int i;
    for(i = 0;i < len;i++) {
        //分配节点
        PNODE newNode = (PNODE)malloc(sizeof(NODE));
        if (newNode == NULL) {
            printf("malloc error");
        }
        printf("please input value:");
        int val;
        scanf("%d", &val);
        newNode->data = val;
        newNode->pNext = NULL;
        tempNode->pNext = newNode;
        tempNode = newNode;
    }
    return pHead;
}
void traverse_list(PNODE pHead) {
    PNODE t = pHead->pNext;
    while(t != NULL) {
        printf("data=%d\n", t->data);
        t = t->pNext;
    }
    return ;
}
PNODE reverse_list(PNODE pHead) {
    PNODE t = pHead->pNext;
    PNODE reverse = NULL;
    PNODE tempNode = NULL;
    while(t != NULL) {
        tempNode = t->pNext;
        if (reverse == NULL) {
            reverse = t;
            reverse->pNext = NULL;
        } else {
            t->pNext = reverse;
            reverse = t;
        }
        t = tempNode;
    }
    pHead->pNext = reverse;
    return pHead;
}
PNODE create_circle_list() {
    //1.首先mallc 一个地址
    PNODE pHead = (PNODE)malloc(sizeof(NODE));
    if (pHead == NULL) {
        printf("malloc error");
    }
    int len;
    printf("please input len:");
    scanf("%d", &len);
    printf("len=%d\n", len);
    PNODE tempNode = pHead;
    int i;
    PNODE circleNode = NULL;
    for(i = 0;i < len;i++) {
        //分配节点
        PNODE newNode = (PNODE)malloc(sizeof(NODE));
        if (newNode == NULL) {
            printf("malloc error");
        }
        printf("please input value:");
        int val;
        scanf("%d", &val);
        newNode->data = val;
        newNode->pNext = NULL;
        tempNode->pNext = newNode;
        tempNode = newNode;

        if (circleNode == NULL && i == 2) {
            circleNode = newNode;
        }
        if (len == i+1) {
            newNode->pNext = circleNode;
        }
    }
    return pHead;
}
int check_circle(PNODE pHead) {
    PNODE t = pHead->pNext;
    PNODE t1 = t;
    while(t != NULL && t1 !=NULL) {
        if (t->data == t1->data) {
            return 1;//表示有环的存在
        }
        printf("%d",t->data);
        t = t->pNext;
        t1 = t1->pNext->pNext;

    }
    return 0;
}

参考资料：

《鏈表》http://yanshinian.com/lianbiao