[juhui-jeong]WEEK 12 Solutions

non-overlapping-intervals/juhui-jeong.java

@@ -0,0 +1,51 @@
+/*
+ * 끝나는 시간 오름차순 정렬
+ */
+class Solution {
+    public int eraseOverlapIntervals(int[][] intervals) {
+        Arrays.sort(intervals, (a,b) -> Integer.compare(a[1], b[1]));
+
+        int removeCntResult = 0;
+        int end = intervals[0][1];
+
+        for (int i = 1; i< intervals.length; i++) {
+            if (intervals[i][0] < end) {
+                removeCntResult += 1;
+            } else {
+                end = intervals[i][1];
+            }
+        }
+        return removeCntResult;
+    }
+}
+
+
+/*
+처음 풀이
+시작 시간 기준 정렬
+class Solution {
+    public int eraseOverlapIntervals(int[][] intervals) {
+        Arrays.sort(intervals, (a,b) -> {
+            if (a[0] != b[0]) return Integer.compare(a[0], b[0]);
+            return Integer.compare(a[1], b[1]);
+        });
+
+        int removeCntResult = 0;
+        int[] cur = intervals[0];
+
+        for (int i = 1; i< intervals.length; i++) {
+            int [] next = intervals[i];
+
+            if (cur[1] > next[0]) {
+                removeCntResult += 1;
+                if (next[1] < cur[1]) {
+                    cur = next;
+                }
+            } else {
+                cur = next;
+            }
+        }
+        return removeCntResult;
+    }
+}
+ */

remove-nth-node-from-end-of-list/juhui-jeong.java

@@ -0,0 +1,49 @@
+/* 
+시간 복잡도: O(N)
+공간 복잡도: O(1)
+*/
+class Solution {
+    public ListNode removeNthFromEnd(ListNode head, int n) {
+        ListNode dummy = new ListNode(0);
+        dummy.next = head;
+
+        ListNode fast = dummy;
+        ListNode slow = dummy;
+
+        for (int i = 0; i <= n; i++) {
+            fast = fast.next;
+        }
+
+        while(fast != null) {
+            fast = fast.next;
+            slow = slow.next;
+        }
+
+        slow.next = slow.next.next;
+
+        return dummy.next;
+    }
+}
+
+/* 
+첫 번째 풀이
+class Solution {
+    public ListNode removeNthFromEnd(ListNode head, int n) {
+        List<ListNode> list = new ArrayList<>();
+
+        while(head != null) {
+            list.add(head);
+            head = head.next;
+        }
+
+        list.remove(list.size()-n);
+        if (list.isEmpty()) return null;
+
+        for (int i = 0; i < list.size()-1; i++) {
+            list.get(i).next = list.get(i+1);
+        }
+        list.get(list.size()-1).next = null;
+        return list.get(0);
+    }
+}
+*/

same-tree/juhui-jeong.java

@@ -0,0 +1,12 @@
+/**
+ * 시간복잡도: O(n)
+ * 공간복잡도: O(h)
+ */
+class Solution {
+    public boolean isSameTree(TreeNode p, TreeNode q) {
+        if (p == null && q == null) return true;
+        if (p == null || q == null) return false;
+        if (p.val != q.val) return false;
+        return isSameTree(p.left, q.left) && isSameTree(p.right, q.right);
+    }
+}