added problem 239

Author: SHA65536

problems/problem0239/max_sliding_window.go

@@ -0,0 +1,51 @@
+package problem0239
+
+import "container/heap"
+
+/*
+You are given an array of integers nums, there is a sliding window of size k which is moving from the very left of the array to the very right.
+You can only see the k numbers in the window.
+Each time the sliding window moves right by one position.
+Return the max sliding window.
+*/
+
+func maxSlidingWindow(nums []int, k int) []int {
+	var pq = MakeHeap(MaxHeap)
+	var res = make([]int, len(nums)-k+1)
+
+	for i := 0; i < k; i++ {
+		heap.Push(pq, [2]int{nums[i], i})
+	}
+
+	res[0] = pq.Peek()[0]
+	for i := k; i < len(nums); i++ {
+		for pq.Len() != 0 && pq.Peek()[1] <= i-k {
+			heap.Pop(pq)
+		}
+		heap.Push(pq, [2]int{nums[i], i})
+		res[i-k+1] = pq.Peek()[0]
+	}
+	return res
+}
+
+type Heap struct {
+	Values   [][2]int
+	LessFunc func([2]int, [2]int) bool
+}
+
+func (h *Heap) Less(i, j int) bool { return h.LessFunc(h.Values[i], h.Values[j]) }
+func (h *Heap) Swap(i, j int)      { h.Values[i], h.Values[j] = h.Values[j], h.Values[i] }
+func (h *Heap) Len() int           { return len(h.Values) }
+func (h *Heap) Peek() [2]int       { return h.Values[0] }
+func (h *Heap) Pop() (v interface{}) {
+	h.Values, v = h.Values[:h.Len()-1], h.Values[h.Len()-1]
+	return v
+}
+func (h *Heap) Push(v interface{}) { h.Values = append(h.Values, v.([2]int)) }
+
+func MakeHeap(less func([2]int, [2]int) bool) *Heap {
+	return &Heap{LessFunc: less}
+}
+
+func MaxHeap(i, j [2]int) bool { return i[0] > j[0] }
+func MinHeap(i, j [2]int) bool { return i[0] < j[0] }

problems/problem0239/max_sliding_window_test.go

@@ -0,0 +1,37 @@
+package problem0239
+
+import (
+	"fmt"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+type TestCase struct {
+	Input    []int
+	K        int
+	Expected []int
+}
+
+var TestCases = []TestCase{
+	{[]int{1, 3, -1, -3, 5, 3, 6, 7}, 3, []int{3, 3, 5, 5, 6, 7}},
+	{[]int{1}, 1, []int{1}},
+}
+
+func TestMaxSlidingWindow(t *testing.T) {
+	assert := assert.New(t)
+
+	for _, tc := range TestCases {
+		want := tc.Expected
+		got := maxSlidingWindow(tc.Input, tc.K)
+		assert.Equal(want, got, fmt.Sprintf("%+v", tc))
+	}
+}
+
+func BenchmarkMaxSlidingWindow(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		for _, tc := range TestCases {
+			maxSlidingWindow(tc.Input, tc.K)
+		}
+	}
+}

readme.md

@@ -158,6 +158,7 @@ Each problem is in it's own directory, with test files. There are helper package
 | 0235 | [Lowest Common Ancestor of a Binary Search Tree](https://leetcode.com/problems/lowest-common-ancestor-of-a-binary-search-tree) | [My Solution](./problems/problem0235) | ✅ |
 | 0236 | [Lowest Common Ancestor of a Binary Tree](https://leetcode.com/problems/lowest-common-ancestor-of-a-binary-tree) | [My Solution](./problems/problem0236) | ✅ |
 | 0237 | [Delete Node in a Linked List](https://leetcode.com/problems/delete-node-in-a-linked-list) | [My Solution](./problems/problem0237) | ✅ |
+| 0239 | [Sliding Window Maximum](https://leetcode.com/problems/sliding-window-maximum) | [My Solution](./problems/problem0239) | ✅ |
 | 0240 | [Search a 2D Matrix II](https://leetcode.com/problems/search-a-2d-matrix-ii/) | [My Solution](./problems/problem0240) | ✅ |
 | 0242 | [Valid Anagram](https://leetcode.com/problems/valid-anagram) | [My Solution](./problems/problem0242) | ✅ |
 | 0258 | [Add Digits](https://leetcode.com/problems/add-digits) | [My Solution](./problems/problem0258) | ✅ |