LeetCode | #21 Merge Two Sorted Lists

public class MergeTwoSortedLists {
	
	public class ListNode {
		int val;
		ListNode next;
		ListNode(int x) {
			val = x;
		    next = null;
		}
	}
	public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
        
		ListNode h1 = new ListNode(0), h2 = h1;
		
		while(l1!=null && l2!=null){
			
			if(l1.val < l2.val){
				h1.next = l1;
				l1 = l1.next;
			}else{
				h1.next = l2;
				l2 = l2.next;
			}
			h1 = h1.next;
		}
		if(l1 == null){
			h1.next = l2;
		}
		if(l2 == null){
			h1.next = l1;
		}
		return h2.next;
    }
}

• 还有一种更屌的方法，递归，也是每次选出最小的节点，不过代码更加简洁

//递归解法，头指针每次指向两个列表中最小的节点，然后递归
	public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
        
		if(l1 == null)
			return l2;
		if(l2 == null)
			return l1;
		ListNode h;
		if(l1.val < l2.val){
			h = l1;
			h.next = mergeTwoLists(l1.next, l2);
		}else{
			h = l2;
			h.next = mergeTwoLists(l1, l2.next);
		}
		return h;
	}