Merge pull request #2298 from se6816/main

[se6816] WEEK 11 solutions

Author: se6816

merge-intervals/se6816.java

@@ -0,0 +1,26 @@
+/**
+	탐욕법을 이용하여, 연산하는 방식
+*/
+class Solution {
+    public int[][] merge(int[][] intervals) {
+        
+        Arrays.sort(intervals, (a,b) -> a[0] - b[0]);
+        
+        List<int[]> result = new ArrayList<>();
+        int startNum = intervals[0][0];
+        int endNum = intervals[0][1];
+        for(int i = 1; i < intervals.length; i++) {
+            if(endNum >= intervals[i][0]) {
+                endNum = Math.max(endNum, intervals[i][1]);
+                continue;
+            }
+                
+            result.add(new int[]{startNum, endNum});
+            startNum = intervals[i][0];
+            endNum = intervals[i][1];
+        }
+        result.add(new int[]{startNum, endNum});
+        
+        return result.toArray(new int[result.size()][]);
+    }
+}

missing-number/se6816.java

@@ -0,0 +1,27 @@
+/**
+    최댓값을 기준으로 배열의 합과 1~N까지의 합을 비교하여 확인하는 방식
+ */
+class Solution {
+    public int missingNumber(int[] nums) {
+        int max = 0;
+        int sum = 0;
+        boolean existsZero = false;
+        for(int i = 0; i < nums.length; i++) {
+            max = Math.max(nums[i], max);
+            sum += nums[i];
+            if(nums[i] == 0){
+                existsZero = true;
+            }
+        }
+
+        int result = (max * (max + 1)) / 2 - sum;
+
+        if(!existsZero) {
+            result = 0;
+        } else if(result == 0) {
+            result = max + 1;
+        }
+
+        return result;
+    }
+}

reorder-list/se6816.java

@@ -0,0 +1,25 @@
+
+class Solution {
+    public void reorderList(ListNode head) {
+        if(head.next == null) return;
+
+        ListNode prev = null;
+        while (true) {
+            ListNode tail = head;
+            while (tail.next != null) {
+                prev = tail;
+                tail = tail.next;
+            }
+            
+            if (prev == head) break;  
+            
+            // tail 이동
+            ListNode headNext = head.next;
+            prev.next = null;
+            head.next = tail;
+            tail.next = headNext;
+            
+            head = headNext;
+        }
+    }
+}