Move all solutions into separate directory (cleanup)

the beginning

solutions/add-two-numbers/Solution.java

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+// Accepted
+// Runtime: 1 ms
+// Memory Usage: 39.3 MB
+// Submitted: January 15th, 2021
+
+/**
+ * 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 a, ListNode b) {
+        ListNode dummy = new ListNode(0);
+        ListNode cur = dummy;
+        int carry = 0;
+        
+        while (a != null || b != null) {
+            int x = (a != null) ? a.val : 0;
+            int y = (b != null) ? b.val : 0;
+            int sum = carry + x + y;
+            
+            carry = sum / 10;
+            cur.next = new ListNode(sum % 10);
+            cur = cur.next;
+            
+            if (a != null) a = a.next;
+            if (b != null) b = b.next;
+        }
+        
+        if (carry > 0)
+            cur.next = new ListNode(carry);
+        
+        return dummy.next;
+    }
+}

solutions/add-two-numbers/meta.json

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+{
+    "name": "Add Two Numbers",
+    "solutions": [
+        {
+            "name": "Java",
+            "path": "Solution.java"
+        }
+    ]
+}