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| 1 | +//原来的代码随想录707设计链表的java代码中单链表的设计中有错误,修正后并对双链表进行了简化和更正,下面是我的java代码 |
| 2 | + |
| 3 | +//单链表 |
| 4 | +class ListNode{ |
| 5 | + int val; |
| 6 | + ListNode next; |
| 7 | + ListNode() {}; |
| 8 | + ListNode(int val){ |
| 9 | + this.val = val; |
| 10 | + } |
| 11 | +} |
| 12 | + |
| 13 | + |
| 14 | +class MyLinkedList { |
| 15 | + |
| 16 | + //记录链表中元素的数量 |
| 17 | + int size; |
| 18 | + //记录链表的虚拟头结点 |
| 19 | + ListNode head; |
| 20 | + |
| 21 | + public MyLinkedList() { |
| 22 | + //初始化操作 |
| 23 | + this.size = 0; |
| 24 | + this.head = new ListNode(0); |
| 25 | + this.head.next = null; |
| 26 | + } |
| 27 | + |
| 28 | + public int get(int index) { |
| 29 | + //判断index是否有效 |
| 30 | + if(index<0 || index>=size){ |
| 31 | + return -1; |
| 32 | + } |
| 33 | + ListNode cur = this.head; |
| 34 | + //index 是可以取到的,因为有虚拟头结点 |
| 35 | + for(int i=0; i<= index; i++){ |
| 36 | + cur = cur.next; |
| 37 | + } |
| 38 | + return cur.val; |
| 39 | + } |
| 40 | + |
| 41 | + public void addAtHead(int val) { |
| 42 | + //等价于在第0个元素前添加 |
| 43 | + addAtIndex(0,val); |
| 44 | + } |
| 45 | + |
| 46 | + public void addAtTail(int val) { |
| 47 | + //等价于在最后一个元素(null)前添加 |
| 48 | + addAtIndex(size,val); |
| 49 | + } |
| 50 | + |
| 51 | + public void addAtIndex(int index, int val) { |
| 52 | + //index大于链表长度 |
| 53 | + if(index>size){ |
| 54 | + return; |
| 55 | + } |
| 56 | + //index小于0 |
| 57 | + if(index<0){ |
| 58 | + index = 0; |
| 59 | + } |
| 60 | + size++; |
| 61 | + //找到前驱 |
| 62 | + ListNode pre = this.head; |
| 63 | + for(int i=0; i<index; i++){ |
| 64 | + pre = pre.next; |
| 65 | + } |
| 66 | + //新建结点 |
| 67 | + ListNode newNode = new ListNode(val); |
| 68 | + newNode.next = pre.next; |
| 69 | + pre.next = newNode; |
| 70 | + } |
| 71 | + |
| 72 | + public void deleteAtIndex(int index) { |
| 73 | + //判断索引是否有效 |
| 74 | + if(index<0 || index>=size){ |
| 75 | + return; |
| 76 | + } |
| 77 | + //删除操作 |
| 78 | + size--; |
| 79 | + ListNode pre = this.head; |
| 80 | + for(int i=0; i<index; i++){ |
| 81 | + pre = pre.next; |
| 82 | + } |
| 83 | + pre.next = pre.next.next; |
| 84 | + |
| 85 | + } |
| 86 | +} |
| 87 | + |
| 88 | +//------------------------------------------------------------------------------------------------------------------------------- |
| 89 | +//双向链表 |
| 90 | +class ListNode{ |
| 91 | + int val; |
| 92 | + ListNode next,prev; |
| 93 | + ListNode() {}; |
| 94 | + ListNode(int val){ |
| 95 | + this.val = val; |
| 96 | + } |
| 97 | +} |
| 98 | + |
| 99 | + |
| 100 | +class MyLinkedList { |
| 101 | + |
| 102 | + //记录链表中元素的数量 |
| 103 | + int size; |
| 104 | + //记录链表的虚拟头结点和尾结点 |
| 105 | + ListNode head,tail; |
| 106 | + |
| 107 | + public MyLinkedList() { |
| 108 | + //初始化操作 |
| 109 | + this.size = 0; |
| 110 | + this.head = new ListNode(0); |
| 111 | + this.tail = new ListNode(0); |
| 112 | + //这一步非常关键,否则在加入头结点的操作中会出现null.next的错误!!! |
| 113 | + head.next=tail; |
| 114 | + tail.prev=head; |
| 115 | + } |
| 116 | + |
| 117 | + public int get(int index) { |
| 118 | + //判断index是否有效 |
| 119 | + if(index<0 || index>=size){ |
| 120 | + return -1; |
| 121 | + } |
| 122 | + ListNode cur = this.head; |
| 123 | + //判断是哪一边遍历时间更短 |
| 124 | + if(index >= size / 2){ |
| 125 | + //tail开始 |
| 126 | + cur = tail; |
| 127 | + for(int i=0; i< size-index; i++){ |
| 128 | + cur = cur.prev; |
| 129 | + } |
| 130 | + }else{ |
| 131 | + for(int i=0; i<= index; i++){ |
| 132 | + cur = cur.next; |
| 133 | + } |
| 134 | + } |
| 135 | + return cur.val; |
| 136 | + } |
| 137 | + |
| 138 | + public void addAtHead(int val) { |
| 139 | + //等价于在第0个元素前添加 |
| 140 | + addAtIndex(0,val); |
| 141 | + } |
| 142 | + |
| 143 | + public void addAtTail(int val) { |
| 144 | + //等价于在最后一个元素(null)前添加 |
| 145 | + addAtIndex(size,val); |
| 146 | + } |
| 147 | + |
| 148 | + public void addAtIndex(int index, int val) { |
| 149 | + //index大于链表长度 |
| 150 | + if(index>size){ |
| 151 | + return; |
| 152 | + } |
| 153 | + //index小于0 |
| 154 | + if(index<0){ |
| 155 | + index = 0; |
| 156 | + } |
| 157 | + size++; |
| 158 | + //找到前驱 |
| 159 | + ListNode pre = this.head; |
| 160 | + for(int i=0; i<index; i++){ |
| 161 | + pre = pre.next; |
| 162 | + } |
| 163 | + //新建结点 |
| 164 | + ListNode newNode = new ListNode(val); |
| 165 | + newNode.next = pre.next; |
| 166 | + pre.next.prev = newNode; |
| 167 | + newNode.prev = pre; |
| 168 | + pre.next = newNode; |
| 169 | + |
| 170 | + } |
| 171 | + |
| 172 | + public void deleteAtIndex(int index) { |
| 173 | + //判断索引是否有效 |
| 174 | + if(index<0 || index>=size){ |
| 175 | + return; |
| 176 | + } |
| 177 | + //删除操作 |
| 178 | + size--; |
| 179 | + ListNode pre = this.head; |
| 180 | + for(int i=0; i<index; i++){ |
| 181 | + pre = pre.next; |
| 182 | + } |
| 183 | + pre.next.next.prev = pre; |
| 184 | + pre.next = pre.next.next; |
| 185 | + } |
| 186 | +} |
| 187 | + |
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