[yhkee0404] WEEK 13 solutions

find-median-from-data-stream/yhkee0404.go

@@ -0,0 +1,52 @@
+type MedianFinder struct {
+    lq Heap
+    rq Heap
+}
+
+type Heap []int // S(n) = O(n)
+
+func (pq Heap) Len() int {return len(pq)}
+func (pq Heap) Less(i, j int) bool {return pq[i] < pq[j]}
+func (pq Heap) Swap(i, j int) {pq[i], pq[j] = pq[j], pq[i]}
+func (pq *Heap) Push(x any) {*pq = append(*pq, x.(int))}
+func (pq *Heap) Pop() any {
+    x := (*pq)[len(*pq) - 1]
+    *pq = (*pq)[: len(*pq) - 1]
+    return x
+}
+
+
+func Constructor() MedianFinder {
+    return MedianFinder{}
+}
+
+
+func (this *MedianFinder) AddNum(num int)  { // T(n) = O(logn)
+    if len(this.rq) != 0 && this.rq[0] <= num {
+        heap.Push(&this.rq, num)
+        if len(this.lq) == len(this.rq) - 1 {
+            heap.Push(&this.lq, - heap.Pop(&this.rq).(int))
+        }
+        return
+    }
+    heap.Push(&this.lq, - num)
+    if len(this.lq) == len(this.rq) + 2 {
+        heap.Push(&this.rq, - heap.Pop(&this.lq).(int))
+    }
+}
+
+
+func (this *MedianFinder) FindMedian() float64 { // T(n) = O(1)
+    if len(this.lq) > len(this.rq) {
+        return float64(- this.lq[0])
+    }
+    return float64(- this.lq[0] + this.rq[0]) / 2
+}
+
+
+/**
+ * Your MedianFinder object will be instantiated and called as such:
+ * obj := Constructor();
+ * obj.AddNum(num);
+ * param_2 := obj.FindMedian();
+ */

insert-interval/yhkee0404.swift

@@ -0,0 +1,29 @@
+class Solution {
+    func insert(_ intervals: [[Int]], _ newInterval: [Int]) -> [[Int]] {
+        var ans: [[Int]] = []
+        var i = 0
+        while i != intervals.count && intervals[i][1] < newInterval[0] {
+            ans.append(intervals[i])
+            i += 1
+        }
+        var newInterval = newInterval
+        if i != intervals.count && intervals[i][0] <= newInterval[0] {
+            newInterval[0] = intervals[i][0]
+            newInterval[1] = max(newInterval[1], intervals[i][1])
+            i += 1
+        }
+        while i != intervals.count && intervals[i][1] <= newInterval[1] {
+            i += 1
+        }
+        if i != intervals.count && intervals[i][0] <= newInterval[1] {
+            newInterval[1] = intervals[i][1]
+            i += 1
+        }
+        ans.append(newInterval)
+        while i != intervals.count {
+            ans.append(intervals[i])
+            i += 1
+        }
+        return ans
+    }
+}

kth-smallest-element-in-a-bst/yhkee0404.scala

@@ -0,0 +1,26 @@
+/**
+ * Definition for a binary tree node.
+ * class TreeNode(_value: Int = 0, _left: TreeNode = null, _right: TreeNode = null) {
+ *   var value: Int = _value
+ *   var left: TreeNode = _left
+ *   var right: TreeNode = _right
+ * }
+ */
+object Solution {
+    def kthSmallest(root: TreeNode, k: Int): Int = {
+        count(root, k, -1)
+    }
+    def count(root: TreeNode, k: Int, n: Int): Int = {
+        if (root == null) {
+            return n
+        }
+        val u = count(root.left, k, n)
+        if (u >= 0) {
+            return u
+        }
+        if (- u == k) {
+            return root.value
+        }
+        count(root.right, k, u - 1)
+    }
+}

lowest-common-ancestor-of-a-binary-search-tree/yhkee0404.rs

@@ -0,0 +1,39 @@
+// Definition for a binary tree node.
+// #[derive(Debug, PartialEq, Eq)]
+// pub struct TreeNode {
+//   pub val: i32,
+//   pub left: Option<Rc<RefCell<TreeNode>>>,
+//   pub right: Option<Rc<RefCell<TreeNode>>>,
+// }
+// 
+// impl TreeNode {
+//   #[inline]
+//   pub fn new(val: i32) -> Self {
+//     TreeNode {
+//       val,
+//       left: None,
+//       right: None
+//     }
+//   }
+// }
+use std::rc::Rc;
+use std::cell::RefCell;
+impl Solution {
+    pub fn lowest_common_ancestor(root: Option<Rc<RefCell<TreeNode>>>, p: Option<Rc<RefCell<TreeNode>>>, q: Option<Rc<RefCell<TreeNode>>>) -> Option<Rc<RefCell<TreeNode>>> {
+        match root.as_ref() {
+            None => None,
+            Some(u) if p.as_ref().map_or(false, |pp| Rc::ptr_eq(u, pp)) => p,
+            Some(u) if q.as_ref().map_or(false, |qq| Rc::ptr_eq(u, qq)) => q,
+            Some(u) => {
+                let u = u.borrow();
+                let left = Self::lowest_common_ancestor(u.left.clone(), p.clone(), q.clone());
+                let right = Self::lowest_common_ancestor(u.right.clone(), p.clone(), q.clone());
+                if left.is_some() && right.is_some() {
+                    root.clone()
+                } else {
+                    left.or(right)
+                }
+            },
+        }
+    }
+}

meeting-rooms/yhkee0404.kt

@@ -0,0 +1,24 @@
+/**
+ * Definition of Interval:
+ * class Interval {
+ *     var start: Int = 0
+ *     var end: Int = 0
+ *     constructor(start: Int, end: Int) {
+ *         this.start = start
+ *         this.end = end
+ *     }
+ * }
+ */
+
+class Solution {
+    /**
+     * @param intervals: an array of meeting time intervals
+     * @return: if a person could attend all meetings
+     */
+    fun canAttendMeetings(intervals: List<Interval?>): Boolean {
+        // Write your code here
+        val sorted = intervals.filterNotNull() // T(n) = O(nlogn)
+            	.sortedBy {it!!.end}
+        return (1 until intervals.size).all {sorted[it].start >= sorted[it - 1].end}
+    }
+}