链表专题

洋仔
506 阅读2分钟

1.合并两个有序链表

/**
 * Definition for singly-linked list.
 * function ListNode(val, next) {
 *     this.val = (val===undefined ? 0 : val)
 *     this.next = (next===undefined ? null : next)
 * }
 */
/**
 * @param {ListNode} l1
 * @param {ListNode} l2
 * @return {ListNode}
 */
var mergeTwoLists = function(l1, l2) {
    var dumpy = new ListNode();
    var p = dumpy;
    while(l1&&l2) {
        if(l1.val<l2.val){
            p.next = l1;
            l1 = l1.next;
        } else {
            p.next = l2;
            l2 = l2.next;
        }
        p = p.next;
    }
    if(l1){
        p.next = l1;
    }
    if(l2){
        p.next = l2;
    }
    return dumpy.next;
};

2.链表中倒数第k个节点

/**
 * Definition for singly-linked list.
 * function ListNode(val) {
 *     this.val = val;
 *     this.next = null;
 * }
 */
/**
 * @param {ListNode} head
 * @param {number} k
 * @return {ListNode}
 */
var getKthFromEnd = function(head, k) {
   var fast = head;
   var slow = head;
   var i=1;
   while(i<=k){
       fast = fast.next;
       i++
   }
   while(fast){
       fast = fast.next;
       slow = slow.next;
   }
   return slow;
};

3.两个链表的第一个公共节点

/**
 * Definition for singly-linked list.
 * function ListNode(val) {
 *     this.val = val;
 *     this.next = null;
 * }
 */

/**
 * @param {ListNode} headA
 * @param {ListNode} headB
 * @return {ListNode}
 */
var getIntersectionNode = function(headA, headB) {
    var lenA = getLen(headA);
    var lenB = getLen(headB)
    while(lenA!=lenB){
        if(lenA>lenB){
            headA = headA.next;
            lenA--;
        }else {
            headB = headB.next;
            lenB--;
        }
    }
    while(headB!=headA){
        headA = headA.next;
        headB = headB.next;
    }
    return headA;
}

var getLen = function(node){
    var temp = node;
    var i=0;
    while(temp){
        temp = temp.next;
        i++;
    }
    return i;
}

4.链表倒置

/**
 * Definition for singly-linked list.
 * function ListNode(val, next) {
 *     this.val = (val===undefined ? 0 : val)
 *     this.next = (next===undefined ? null : next)
 * }
 */
/**
 * @param {ListNode} head
 * @return {ListNode}
 */
var reverseList = function(head) {

    var pre = null;
    var cur = head;
    while(cur){
        var temp = cur.next;
        cur.next = pre;
        pre = cur;
        cur = temp;
    }
    return pre;
};

5.环形链表及其环

/**
 * Definition for singly-linked list.
 * function ListNode(val) {
 *     this.val = val;
 *     this.next = null;
 * }
 */

/**
 * @param {ListNode} head
 * @return {ListNode}
 */
var detectCycle = function(head) {
    //set集合法
    // var contains =new Set();
    // var temp = head;
    // while(temp){
    //     if(contains.has(temp)){
    //         return temp;
    //     }
    //     contains.add(temp);
    //     temp = temp.next;
    // }
    // return null
    if(head==null){
        return null;
    }
    var fast = head;
    var slow = head;
    var ptr = head;
    while(fast){
        if(fast.next==null){
            return null;
        }
        fast = fast.next.next;
        slow = slow.next;
        if(fast==slow){
            while(ptr!=slow){
                ptr = ptr.next;
                slow = slow.next;
            }
            return ptr;
        }
    }
    return null;
};

6.反转链表 II

/**
 * Definition for singly-linked list.
 * function ListNode(val, next) {
 *     this.val = (val===undefined ? 0 : val)
 *     this.next = (next===undefined ? null : next)
 * }
 */
/**
 * @param {ListNode} head
 * @param {number} left
 * @param {number} right
 * @return {ListNode}
 */
var reverseBetween = function(head, left, right) {
   
   var dumpy = new ListNode();
   dumpy.next = head;
   var pre = dumpy;
   var i=1;
   while(pre&&i<left){
       pre = pre.next;
       i++;
   }
   var rightNode = pre.next;
   var j=1;
   while(rightNode&&j<(right-left+1)){
    rightNode = rightNode.next;
    j++;   
   }
  var leftNode = pre.next;
  var temp = rightNode.next;
  pre.next = null;
  rightNode.next = null;
  pre.next = reverse(leftNode);
  leftNode.next = temp;
  return dumpy.next;
};
var reverse = function(root) {
    if(!root) {
        return root;
    }
    var cur = root;
    var pre = null;
    while(cur){
        var temp = cur.next;
        cur.next = pre;
        pre = cur;
        cur = temp;
    }
    return pre;
}

7.删除链表的倒数第 N 个结点

/**
 * Definition for singly-linked list.
 * function ListNode(val, next) {
 *     this.val = (val===undefined ? 0 : val)
 *     this.next = (next===undefined ? null : next)
 * }
 */
/**
 * @param {ListNode} head
 * @param {number} n
 * @return {ListNode}
 */
var removeNthFromEnd = function(head, n) {
   var fast = head;
   var dumpy = new ListNode();
   dumpy.next = head;
   var slow = dumpy;
   var i=1;
   while(fast&&i<=n){
       fast = fast.next;
       i++;
   }
   while(fast){
       slow = slow.next;
       fast = fast.next;
   }
   slow.next = slow.next.next;
   return dumpy.next;
};

8.两个链表之和

/**
 * Definition for singly-linked list.
 * function ListNode(val, next) {
 *     this.val = (val===undefined ? 0 : val)
 *     this.next = (next===undefined ? null : next)
 * }
 */
/**
 * @param {ListNode} l1
 * @param {ListNode} l2
 * @return {ListNode}
 */
var addTwoNumbers = function(l1, l2) {
    var dumpy = new ListNode();
    var temp = dumpy;
    var extra = 0;
    while(l1||l2){
        var n1 = l1!=null?l1.val:0;
        var n2 = l2!=null?l2.val:0;
        var sum = n1+n2+extra;
        extra = Math.floor(sum/10);
        temp.next = new ListNode(sum%10);
        temp = temp.next
        if(l1){
            l1 = l1.next;
        }
        if(l2){
            l2 = l2.next;
        }
    }
    if(extra){
        temp.next = new ListNode(extra);
    }
    return dumpy.next;
};

9.合并K个升序链表

/**
 * Definition for singly-linked list.
 * function ListNode(val, next) {
 *     this.val = (val===undefined ? 0 : val)
 *     this.next = (next===undefined ? null : next)
 * }
 */
/**
 * @param {ListNode[]} lists
 * @return {ListNode}
 */
var mergeKLists = function(lists) {
   if(lists.length==0){
       return null;
   }
   var temp = lists[0];
   for(var i=1;i<lists.length;i++){
       temp = mergeLinkTwo(temp,lists[i])
   }
   return temp;
};

var mergeLinkTwo = function(l1,l2){
    var dumpy = new ListNode();
    var ptr = dumpy;
    while(l1&&l2){
        if(l1.val<l2.val){
            ptr.next = l1;
            l1 = l1.next;
        } else {
            ptr.next = l2;
            l2 = l2.next;
        }
        ptr = ptr.next;
    }
    if(l1){
        ptr.next = l1;
    }
    if(l2){
        ptr.next = l2;
    }
    return dumpy.next;
}

10.排序链表(归并法)

/**
 * Definition for singly-linked list.
 * function ListNode(val, next) {
 *     this.val = (val===undefined ? 0 : val)
 *     this.next = (next===undefined ? null : next)
 * }
 */
/**
 * @param {ListNode} head
 * @return {ListNode}
 */
var sortList = function(head) {
    if(!head||head.next==null){
        return head;
    }
   var fast = head;
   var slow = head;
   while(fast&&fast.next&&fast.next.next){
       fast = fast.next.next;
       slow = slow.next;
   }
  var right = sortList(slow.next);
  slow.next = null;
  var left = sortList(head);
  return mergLink(left,right)
};

var mergLink = function(l1,l2){
    var dumpy = new ListNode();
    var ptr = dumpy;
    while(l1&&l2){
        if(l1.val<l2.val){
            ptr.next = l1;
            l1 = l1.next;
        } else {
            ptr.next = l2;
            l2 = l2.next;
        }
        ptr = ptr.next;
    }
    if(l1){
        ptr.next = l1;
    }
    if(l2){
        ptr.next = l2;
    }
    return dumpy.next;
}

11.K 个一组翻转链表

/**
 * Definition for singly-linked list.
 * function ListNode(val, next) {
 *     this.val = (val===undefined ? 0 : val)
 *     this.next = (next===undefined ? null : next)
 * }
 */
/**
 * @param {ListNode} head
 * @param {number} k
 * @return {ListNode}
 */
var reverseKGroup = function(head, k) {
    var dumpy = new ListNode();
    dumpy.next = head;
    var pre = dumpy;
    var rightNode = dumpy;
    while(rightNode){
        var i=0;
        while(rightNode&&i<k){
            rightNode = rightNode.next;
            i++;
        }
        if(rightNode){
        var temp = rightNode.next;
        var leftNode = pre.next;
            rightNode.next = null;
            pre.next = reverse(leftNode);
            leftNode.next = temp;

            pre = leftNode;
            rightNode = leftNode
        }
        
    }
    return dumpy.next;
};
var reverse = function(root){
    if(!root){
        return root;
    }
    var pre = null;
    var cur = root;
    while(cur){
        var temp = cur.next;
        cur.next = pre;
        pre = cur;
        cur = temp;
    }
    return pre;
}
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