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package Lists;

/**

* 合并排序列表

*/

class ListNode {

int val;

ListNode next;

ListNode() {}

ListNode(int val) { this.val = val; }

ListNode(int val, ListNode next) { this.val = val; this.next = next; }

}

public class MergeTwoSortedLists_21 {

public static ListNode mergeTwoLists(ListNode l1, ListNode l2) {

if(l1==null) return l2;

if(l2==null) return l1;

ListNode res,head;

if(l1.val<l2.val) {

res=l1;

head=l1;

l1=l1.next;

}else{

res=l2;

head=l2;

l2=l2.next;

}

while(l1!=null&&l2!=null){

if(l1.val<l2.val){

res.next=l1;

res=res.next;

l1=l1.next;

} else{

res.next=l2;

res=res.next;

l2=l2.next;

}

// else{ //先前写成res.next=l1;res.next.next=l2;错误，这样使得链表不断循环

// res.next=l1;

// res=res.next;

// l1=l1.next;

// res.next=l2;

// res=res.next;

// l2=l2.next;

// }

}

if(l1!=null) res.next=l1;

if(l2!=null) res.next=l2;

return head;

}

/*************************************************************************************/

public static ListNode mergeTwoLists_v2(ListNode l1, ListNode l2) {

ListNode res=new ListNode(0);

ListNode head=res;

while(l1!=null&&l2!=null){

if(l1.val<l2.val){

res.next=l1;

l1=l1.next;

} else{

res.next=l2;

l2=l2.next;

}

res=res.next;

}

res.next=l1!=null?l1:l2;

return head.next;

}

/*************************************************************************************/

public static ListNode mergeTwoLists_v3(ListNode l1, ListNode l2) {

if(l1==null) return l2;

if(l2==null) return l1;

if(l1.val<l2.val){

l1.next=mergeTwoLists_v3(l1.next,l2);

return l1;

}else{

l2.next=mergeTwoLists_v3(l1,l2.next);

return l2;

}

}

/*

* Runtime: 0 ms, faster than 100.00% of Java online submissions for Merge Two Sorted Lists.

* Memory Usage: 39 MB, less than 74.53% of Java online submissions for Merge Two Sorted Lists.

*/

public static void main(String[] args) {

int[] a={1,2,4};

int[] b={1,3,4};

ListNode l1=new ListNode(1);

ListNode l2=new ListNode(1);

ListNode headl1=l1;

ListNode headl2=l2;

for(int i=1;i<a.length;i++){

ListNode t=new ListNode(a[i]);

l1.next=t;

l1=l1.next;

}

for(int i=1;i<b.length;i++){

ListNode t=new ListNode(b[i]);

l2.next=t;

l2=l2.next;

}

ListNode res=mergeTwoLists_v3(headl1,headl2);

while (res!=null){

System.out.println(res.val);

res=res.next;

}

}

}