博客记录-day139-力扣+场景题

一、力扣

1、字符串相加

java 复制代码

class Solution {
    public String addStrings(String num1, String num2) {
        StringBuilder res = new StringBuilder();
        int i = num1.length() - 1, j = num2.length() - 1, carry = 0;
        while(i >= 0 || j >= 0){
            int n1 = i >= 0 ? num1.charAt(i) - '0' : 0;
            int n2 = j >= 0 ? num2.charAt(j) - '0' : 0;
            int tmp = n1 + n2 + carry;
            carry = tmp / 10;
            res.append(tmp % 10);
            i--; j--;
        }
        if(carry == 1) res.append(1);
        return res.reverse().toString();
    }
}

2、重排链表

143. 重排链表

java 复制代码

class Solution {
    public void reorderList(ListNode head) {
        ListNode sec=findmid(head);
        ListNode head2=reverse(sec);
        ListNode cur=head;
        while(head2!=null){
            ListNode head2next=head2.next;
            head2.next=null;
            ListNode cop=cur.next;
            cur.next=head2;
            head2.next=cop;
            cur=cop;
            head2=head2next;
        }
    }
    public ListNode findmid(ListNode head){
        ListNode fast=head;
        ListNode slow=head;
        while(fast!=null&&fast.next!=null){
            fast=fast.next.next;
            slow=slow.next;
        }
        ListNode res=slow.next;
        slow.next=null;
        return res;
    }
    public ListNode reverse(ListNode head){
        ListNode pre=null;
        while(head!=null){
            ListNode nextHead=head.next;
            head.next=pre;
            pre=head;
            head=nextHead;
        }
        return pre;
    }
}

3、相交链表

160. 相交链表

java 复制代码

public class Solution {
    public ListNode getIntersectionNode(ListNode headA, ListNode headB) {
        ListNode temp1=headA,temp2=headB;
        while(temp1!=temp2){
            temp1=(temp1==null?headB:temp1.next);
            temp2=(temp2==null?headA:temp2.next);
        }
        return temp1;
    }
}