feat: 2025-10-27打卡

445.add-two-numbers-ii.java

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+/*
+ * @lc app=leetcode id=445 lang=java
+ *
+ * [445] Add Two Numbers II
+ */
+
+// @lc code=start
+/**
+ * Definition for singly-linked list.
+ * public class ListNode {
+ *     int val;
+ *     ListNode next;
+ *     ListNode() {}
+ *     ListNode(int val) { this.val = val; }
+ *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
+ * }
+ */
+class Solution {
+    public ListNode addTwoNumbers(ListNode l1, ListNode l2) {
+        l1 = reverse(l1);
+        l2 = reverse(l2);
+        return reverse(addByLittleEnd(l1, l2));
+    }
+
+    private ListNode addByLittleEnd(ListNode l1, ListNode l2) {
+        ListNode dummy = new ListNode(0), tail = dummy;
+        dummy.next = null;
+        boolean flow = false;
+        while(l1 != null || l2 != null) {
+            int v1 = l1==null?0:l1.val;
+            int v2 = l2==null?0:l2.val;
+            int v = v1 + v2 + (flow?1:0);
+            flow = v>=10;
+            ListNode tmp = new ListNode(v%10, null);
+            tail.next = tmp;
+            tail = tail.next;
+            tail.next = null;
+            if(l1 != null) {
+                l1 = l1.next;
+            } 
+            if(l2 != null) {
+                l2 = l2.next;
+            }
+        }
+        if(flow) {
+            ListNode tmp = new ListNode(1, null);
+            tail.next = tmp;
+            tail = tail.next;
+            tail.next = null;
+        }
+        return dummy.next;
+    }
+
+    private ListNode reverse(ListNode l) {
+        if(l == null) {
+            return l;
+        }
+        ListNode dummy = new ListNode(0), tmp;
+        dummy.next = null;
+        while(l != null) {
+            tmp = l.next;
+            l.next = dummy.next;
+            dummy.next = l;
+            l = tmp;   
+        }
+        return dummy.next;
+    }
+}
+// @lc code=end
+