Linux学习—数据结构（链表2）

1.单向链表

6.链表的查找

在链表中找到指定的第一个元素

• 沿用遍历思想，每次访问一个节点元素判断是否为要找的节点
• 符合条件返回该节点地址
• 到最后没有找到符号条件的节NULL

linknode *find_linklist(linknode *phead, datatype tmpdata)
{linknode *ptmpnode = NULL;ptmpnode = phead->pnext;while(ptmpnode != NULL){if(ptmpnode->data == tmpdata){return ptmpnode;}else{ptmpnode = ptmpnode->pnext;}}return NULL;
}

7.链表的修改

沿用遍历思想，找到需要修改的节点

/*更换链表老元素为新元素*/
int update_linklist(linknode *phead, datatype olddata, datatype newdata)
{linknode *ptmpnode = phead->pnext;while(ptmpnode != NULL){if(ptmpnode->data == olddata){ptmpnode->data = newdata;ptmpnode = ptmpnode->pnext;}else{ ptmpnode = ptmpnode->pnext;   }}return 0;
}

8.尾插法

在链表结尾插入一个元素

• 申请节点空间
• 将数据存放到节点中
• 将节点中地址赋值为NULL
• 找到最后一个节点
• 最后一个节点的pnext赋值为新申请节点

int insert_tail_linklist(linknode *phead, datatype tmpdata)
{linknode *ptmpnode = NULL;linknode *pnewnode = NULL;ptmpnode = phead;       //从空白节点开始找pnewnode = malloc(sizeof(linknode));if(NULL == pnewnode){perror("fail to malloc");return -1;}while(ptmpnode->pnext != NULL){ptmpnode = ptmpnode->pnext;}pnewnode->data = tmpdata;pnewnode->pnext = NULL;ptmpnode->pnext = pnewnode;return 0;
}

 9.链表的销毁

• 定义两个指针pfreenode和ptmpnode都指向头结点
• ptmpnode向后走
• 再释放pfreenode指向的节点
• 再将pfreenode指向ptmpnode指向的空间

void destroy_linklist(linknode **pphead)
{linknode *ptmpnode = NULL;linknode *pfreenode = NULL;pfreenode = *pphead;ptmpnode = *pphead;while(ptmpnode != NULL){ptmpnode = ptmpnode->pnext;free(pfreenode);pfreenode = ptmpnode;}*pphead = NULL;return;
}

10.查找链表的中间节点

• 快指针每次走2步，慢指针每次走1步
• 快指针走到末尾，慢指针走到中间

linknode *find_midnode(linknode *phead)
{linknode *pfast = NULL;linknode *pslow = NULL;pfast = pslow = phead->pnext;while(pfast != NULL){pfast = pfast->pnext;if(pfast == NULL){break;}        pfast = pfast->pnext;if(pfast == NULL){break;}pslow = pslow->pnext;}return pslow;
}

11.查找链表倒数第k个节点

• 快指针先走k步
• 慢指针和快指针每次走一步
• 快指针到达末尾，慢指针少走k步，即倒数第k个元素

/*查找链表倒数第k个节点*/
linknode *find_last_kth_node(linknode *phead, int k)
{int i = 0;linknode *pfast = NULL;linknode *pslow = NULL;pfast = phead->pnext;pslow = phead->pnext;for(i = 0; i < k && pfast != NULL; i++){pfast = pfast->pnext;}if(pfast == NULL){return NULL;}while(pfast != NULL){pfast = pfast->pnext;pslow = pslow->pnext;}return pslow;
}

12.不知道头节点地址，如何删除链表中间节点

• 将指针指向的下一个节点的值覆盖当前节点的值
• 删除下一个节点

void delete_linknode(linknode *ptmpnode)
{linknode *pnextnode = NULL;pnextnode = ptmpnode->pnext;ptmpnode->data = pnextnode->data;ptmpnode->pnext = pnextnode->pnext;free(pnextnode);return;
}

13.链表的倒置

将链表所以元素倒置

• 将原链表断开
• 将所有的元素依次使用头插法插入

void reverse_linklist(linknode *phead)
{linknode *ptmpnode = NULL;linknode *pinsertnode = NULL;//将链表从头结点断开ptmpnode = phead->pnext;phead->pnext = NULL;//依次将所有元素使用头插法插入链表while(ptmpnode != NULL){pinsertnode = ptmpnode;ptmpnode = ptmpnode->pnext;pinsertnode->pnext = phead->pnext;phead->pnext = pinsertnode;}return;
}

14.链表的排序

冒号排序

• 采用冒号排序思想，定义两个指针，相邻两个元素比较
• 指针循环向后走，直到ptmnode2为NULL，即等于pend，循环停止
• pend赋值为ptmpnode1的节点地址
• 下一轮就可以少比一次

void bubble_sort_linklist(linknode *phead)
{linknode *ptmpnode1 = NULL;linknode *ptmpnode2 = NULL;linknode *pend = NULL;datatype tmpdata;if(NULL == phead->pnext || NULL == phead->pnext->pnext){return;}while(1){ptmpnode1 = phead->pnext;ptmpnode2 = phead->pnext->pnext;if(ptmpnode2 == pend){break;}while(ptmpnode2 != pend){if(ptmpnode1->data > ptmpnode2->data){tmpdata = ptmpnode1->data;ptmpnode1->data = ptmpnode2->data;ptmpnode2->data = tmpdata;}ptmpnode1 = ptmpnode1->pnext;ptmpnode2 = ptmpnode2->pnext;}pend = ptmpnode1;}return;
}

选择排序

• pswapnode指向要交换的节点
• pminnode假设的最小值
• ptmpnode和后续节点比较

void select_sort_linklist(linknode *phead)
{linknode *pminnode = NULL;linknode *pswapnode = NULL;linknode *ptmpnode = NULL;datatype tmpdata;if(NULL == phead->pnext || NULL == phead->pnext->pnext){return;}pswapnode = phead->pnext;while(pswapnode->pnext != NULL){pminnode = pswapnode;ptmpnode = pswapnode->pnext;while(ptmpnode != NULL){if(ptmpnode->data < pminnode->data){pminnode = ptmpnode;}ptmpnode = ptmpnode->pnext;}if(pminnode != pswapnode){tmpdata = pminnode->data;pminnode->data = pswapnode->data;pswapnode->data = tmpdata;}pswapnode = pswapnode->pnext;}return;
}

15.判断链表是否有环

• 判断链表是否有环
• 计算环长
• 找到环的入口位置

判断是否有环

• 定义两个指针：快指针（每次2步）和慢指针（每次走1步）
• 快指针-慢指针 == 环长即相遇， 快指针和慢指针相等即为链表有环

计算环长

• 定义一个指针从环相遇开始走一圈，知道走到该节点为止
• 每走一个节点计数，最终得到环长

获得环的入口位置

• 定义一个指针，从相遇点开始每次走一步，定义一个指针，从开头每次走一步
• 两个指针相遇即为环入口

2.双向链表

1.创建空链表

参考单向链表的创建

linknode *creat_empty_linlist(void)
{linknode *ptmpnode = NULL;ptmpnode = malloc(sizeof(linknode));if(NULL == ptmpnode){perror("fail to malloc");return NULL;}ptmpnode->pnext = NULL;ptmpnode->ppre = NULL;return ptmpnode;
}