[njngwn] Week 13 Solutions

kth-smallest-element-in-a-bst/njngwn.java

@@ -0,0 +1,37 @@
+/**
+ * Definition for a binary tree node.
+ * public class TreeNode {
+ *     int val;
+ *     TreeNode left;
+ *     TreeNode right;
+ *     TreeNode() {}
+ *     TreeNode(int val) { this.val = val; }
+ *     TreeNode(int val, TreeNode left, TreeNode right) {
+ *         this.val = val;
+ *         this.left = left;
+ *         this.right = right;
+ *     }
+ * }
+ */
+class Solution {
+    int cnt = 0;
+    int result = 0;
+
+    public int kthSmallest(TreeNode root, int k) {
+        cnt = k;
+        traverseInOrder(root);
+        return result;
+    }
+
+    public void traverseInOrder (TreeNode node) {
+        if (node == null) return;
+
+        if (node.left != null) traverseInOrder(node.left);
+        cnt--;
+        if (cnt == 0) {
+            result = node.val;
+            return;
+        }
+        if (node.right != null) traverseInOrder(node.right);
+    }
+}

lowest-common-ancestor-of-a-binary-search-tree/njngwn.java

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+/**
+ * Definition for a binary tree node.
+ * public class TreeNode {
+ *     int val;
+ *     TreeNode left;
+ *     TreeNode right;
+ *     TreeNode(int x) { val = x; }
+ * }
+ */
+
+class Solution {
+    public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) {
+        if (root.val == p.val || root.val == q.val) return root;
+
+        if (p.val < root.val && q.val < root.val) {
+            return lowestCommonAncestor(root.left, p, q);
+        } else if (p.val > root.val && q.val > root.val) {
+            return lowestCommonAncestor(root.right, p, q);
+        } else {
+            return root;
+        }
+    }
+}

meeting-rooms/njngwn.java

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+/**
+ * Definition of Interval:
+ * public class Interval {
+ *     int start, end;
+ *     Interval(int start, int end) {
+ *         this.start = start;
+ *         this.end = end;
+ *     }
+ * }
+ */
+
+public class Solution {
+    /**
+     * @param intervals: an array of meeting time intervals
+     * @return: if a person could attend all meetings
+     */
+    public boolean canAttendMeetings(List<Interval> intervals) {
+        // Write your code here
+        intervals.sort((a, b) -> a.start - b.start);    // sort by start time
+
+        int prevEndTime = 0;
+        for (Interval meeting : intervals) {
+            if (meeting.start < prevEndTime) {
+                return false;
+            }
+            prevEndTime = meeting.end;
+        }
+        return true;
+    }
+}