学习链表1 Leetcode203

203. 移除链表元素

这种一般有两种方法，第一种就是先判断头节点，之后判断除了头节点以外其他节点

struct ListNode* removeElements(struct ListNode* head, int val){
    while (NULL != head && head->val == val) {
        head = head->next;
    }

    if (NULL == head) {
        return head;
    }

    struct ListNode* pre = head;
    while (pre->next != NULL) {
        /* 找到值为 val 的节点，并将其删除 */
        if (pre->next->val == val) {
            pre->next = pre->next->next;   
        } else {
            /* 没找到，则继续遍历查找 */
            pre = pre->next;
        }
    }
    return head;
}

第二种就是构造一个虚拟头节点

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     struct ListNode *next;
 * };
 */


struct ListNode* removeElements(struct ListNode* head, int val){
    typedef struct ListNode ListNode;
    ListNode *shead;
    shead = (ListNode *)malloc(sizeof(ListNode));
    shead->next = head;
    ListNode *cur = shead;
    while(cur->next != NULL){
        if (cur->next->val == val){
            ListNode *tmp = cur->next;
            cur->next = cur->next->next;
            free(tmp);
        }
        else{
            cur = cur->next;
        }
    }
    head = shead->next;
    free(shead);
    return head;
}