[std-freejia] Week11 solutions

missing-number/std-freejia.java

@@ -0,0 +1,16 @@
+class Solution {
+    public int missingNumber(int[] nums) {
+
+        int totalSum = 0;      
+        // 0부터 nums.length 까지 전부 합    
+        for (int i = 0; i <= nums.length; i++) {
+            totalSum += i;
+        }
+        // 0부터 n까지 전부 합 
+        for (int i = 0; i < nums.length; i++) {
+            totalSum -= nums[i];
+        }
+
+        return totalSum;
+    }
+}

reorder-list/std-freejia.py

@@ -0,0 +1,29 @@
+class Solution:
+    def reorderList(self, head: Optional[ListNode]) -> None:
+        if not head or not head.next: 
+            return
+        # 중간 노드 찾기 
+        slow, fast = head, head 
+        while fast and fast.next: 
+            slow = slow.next # 1칸 
+            fast = fast.next.next # 2칸 
+
+        # 뒤 구간들을 뒤집는다 
+        prev, cur = None, slow.next 
+        # 중간노드 기준으로 앞 구간만 떼어놓는다 
+        slow.next = None
+
+        while cur: 
+            nxt = cur.next # 다음 노드 기억 
+            cur.next = prev
+            prev = cur 
+            cur = nxt
+        # 앞, 뒤 구간들을 병합 
+        first, second = head, prev 
+        while second: 
+            n1, n2 = first.next, second.next
+            first.next = second
+            second.next = n1
+            first, second = n1, n2
+
+