Add solution 0284、0703

leetcode/0173.Binary-Search-Tree-Iterator/173. Binary Search Tree Iterator.go

@@ -1,8 +1,8 @@
 package leetcode
 
-import "container/heap"
-
 import (
+	"container/heap"
+
 	"github.com/halfrost/LeetCode-Go/structures"
 )
 

leetcode/0284.Peeking-Iterator/284. Peeking Iterator.go

@@ -0,0 +1,53 @@
+package leetcode
+
+//Below is the interface for Iterator, which is already defined for you.
+
+type Iterator struct {
+}
+
+func (this *Iterator) hasNext() bool {
+	// Returns true if the iteration has more elements.
+	return true
+}
+
+func (this *Iterator) next() int {
+	// Returns the next element in the iteration.
+	return 0
+}
+
+type PeekingIterator struct {
+	nextEl int
+	hasEl  bool
+	iter   *Iterator
+}
+
+func Constructor(iter *Iterator) *PeekingIterator {
+	return &PeekingIterator{
+		iter: iter,
+	}
+}
+
+func (this *PeekingIterator) hasNext() bool {
+	if this.hasEl {
+		return true
+	}
+	return this.iter.hasNext()
+}
+
+func (this *PeekingIterator) next() int {
+	if this.hasEl {
+		this.hasEl = false
+		return this.nextEl
+	} else {
+		return this.iter.next()
+	}
+}
+
+func (this *PeekingIterator) peek() int {
+	if this.hasEl {
+		return this.nextEl
+	}
+	this.hasEl = true
+	this.nextEl = this.iter.next()
+	return this.nextEl
+}

leetcode/0284.Peeking-Iterator/284. Peeking Iterator_test.go

@@ -0,0 +1,9 @@
+package leetcode
+
+import (
+	"testing"
+)
+
+func Test_Problem284(t *testing.T) {
+
+}

leetcode/0284.Peeking-Iterator/README.md

@@ -0,0 +1,87 @@
+# [284. Peeking Iterator](https://leetcode.com/problems/peeking-iterator/)
+
+## 题目
+
+Given an Iterator class interface with methods: `next()` and `hasNext()`, design and implement a PeekingIterator that support the `peek()` operation -- it essentially peek() at the element that will be returned by the next call to next().
+
+**Example:**
+
+```
+Assume that the iterator is initialized to the beginning of the list: [1,2,3].
+
+Call next() gets you 1, the first element in the list.
+Now you call peek() and it returns 2, the next element. Calling next() after that still return 2. 
+You call next() the final time and it returns 3, the last element. 
+Calling hasNext() after that should return false.
+```
+
+**Follow up**: How would you extend your design to be generic and work with all types, not just integer?
+
+## 题目大意
+
+给定一个迭代器类的接口，接口包含两个方法： next() 和 hasNext()。设计并实现一个支持 peek() 操作的顶端迭代器 -- 其本质就是把原本应由 next() 方法返回的元素 peek() 出来。
+
+> peek() 是偷看的意思。偷偷看一看下一个元素是什么，但是并不是 next() 访问。
+
+## 解题思路
+
+- 简单题。在 PeekingIterator 内部保存 2 个变量，一个是下一个元素值，另一个是是否有下一个元素。在 next() 操作和 hasNext() 操作时，访问保存的这 2 个变量。peek() 操作也比较简单，判断是否有下一个元素，如果有，即返回该元素值。这里实现了迭代指针不移动的功能。如果没有保存下一个元素值，即没有 peek() 偷看，next() 操作继续往后移动指针，读取后一位元素。
+- 这里复用了是否有下一个元素值，来判断 hasNext() 和 peek() 操作中不移动指针的逻辑。
+
+## 代码
+
+```go
+package leetcode
+
+//Below is the interface for Iterator, which is already defined for you.
+
+type Iterator struct {
+}
+
+func (this *Iterator) hasNext() bool {
+	// Returns true if the iteration has more elements.
+	return true
+}
+
+func (this *Iterator) next() int {
+	// Returns the next element in the iteration.
+	return 0
+}
+
+type PeekingIterator struct {
+	nextEl int
+	hasEl  bool
+	iter   *Iterator
+}
+
+func Constructor(iter *Iterator) *PeekingIterator {
+	return &PeekingIterator{
+		iter: iter,
+	}
+}
+
+func (this *PeekingIterator) hasNext() bool {
+	if this.hasEl {
+		return true
+	}
+	return this.iter.hasNext()
+}
+
+func (this *PeekingIterator) next() int {
+	if this.hasEl {
+		this.hasEl = false
+		return this.nextEl
+	} else {
+		return this.iter.next()
+	}
+}
+
+func (this *PeekingIterator) peek() int {
+	if this.hasEl {
+		return this.nextEl
+	}
+	this.hasEl = true
+	this.nextEl = this.iter.next()
+	return this.nextEl
+}
+```

leetcode/0703.Kth-Largest-Element-in-a-Stream/703. Kth Largest Element in a Stream.go

@@ -0,0 +1,38 @@
+package leetcode
+
+import (
+	"container/heap"
+	"sort"
+)
+
+type KthLargest struct {
+	sort.IntSlice
+	k int
+}
+
+func Constructor(k int, nums []int) KthLargest {
+	kl := KthLargest{k: k}
+	for _, val := range nums {
+		kl.Add(val)
+	}
+	return kl
+}
+
+func (kl *KthLargest) Push(v interface{}) {
+	kl.IntSlice = append(kl.IntSlice, v.(int))
+}
+
+func (kl *KthLargest) Pop() interface{} {
+	a := kl.IntSlice
+	v := a[len(a)-1]
+	kl.IntSlice = a[:len(a)-1]
+	return v
+}
+
+func (kl *KthLargest) Add(val int) int {
+	heap.Push(kl, val)
+	if kl.Len() > kl.k {
+		heap.Pop(kl)
+	}
+	return kl.IntSlice[0]
+}

leetcode/0703.Kth-Largest-Element-in-a-Stream/703. Kth Largest Element in a Stream_test.go

@@ -0,0 +1,15 @@
+package leetcode
+
+import (
+	"fmt"
+	"testing"
+)
+
+func Test_Problem703(t *testing.T) {
+	obj := Constructor(3, []int{4, 5, 8, 2})
+	fmt.Printf("Add 7 = %v\n", obj.Add(3))
+	fmt.Printf("Add 7 = %v\n", obj.Add(5))
+	fmt.Printf("Add 7 = %v\n", obj.Add(10))
+	fmt.Printf("Add 7 = %v\n", obj.Add(9))
+	fmt.Printf("Add 7 = %v\n", obj.Add(4))
+}

leetcode/0703.Kth-Largest-Element-in-a-Stream/README.md

@@ -0,0 +1,93 @@
+# [703. Kth Largest Element in a Stream](https://leetcode.com/problems/kth-largest-element-in-a-stream/)
+
+## 题目
+
+Design a class to find the `kth` largest element in a stream. Note that it is the `kth` largest element in the sorted order, not the `kth` distinct element.
+
+Implement `KthLargest` class:
+
+- `KthLargest(int k, int[] nums)` Initializes the object with the integer `k` and the stream of integers `nums`.
+- `int add(int val)` Returns the element representing the `kth` largest element in the stream.
+
+**Example 1:**
+
+```
+Input
+["KthLargest", "add", "add", "add", "add", "add"]
+[[3, [4, 5, 8, 2]], [3], [5], [10], [9], [4]]
+Output
+[null, 4, 5, 5, 8, 8]
+
+Explanation
+KthLargest kthLargest = new KthLargest(3, [4, 5, 8, 2]);
+kthLargest.add(3);   // return 4
+kthLargest.add(5);   // return 5
+kthLargest.add(10);  // return 5
+kthLargest.add(9);   // return 8
+kthLargest.add(4);   // return 8
+
+```
+
+**Constraints:**
+
+- `1 <= k <= 104`
+- `0 <= nums.length <= 104`
+- `104 <= nums[i] <= 104`
+- `104 <= val <= 104`
+- At most `104` calls will be made to `add`.
+- It is guaranteed that there will be at least `k` elements in the array when you search for the `kth` element.
+
+## 题目大意
+
+设计一个找到数据流中第 k 大元素的类（class）。注意是排序后的第 k 大元素，不是第 k 个不同的元素。请实现 KthLargest 类：
+
+- KthLargest(int k, int[] nums) 使用整数 k 和整数流 nums 初始化对象。
+- int add(int val) 将 val 插入数据流 nums 后，返回当前数据流中第 k 大的元素。
+
+## 解题思路
+
+- 读完题就能明白这一题考察的是最小堆。构建一个长度为 K 的最小堆，每次 pop 堆首(堆中最小的元素)，维护堆首即为第 K 大元素。
+- 这里有一个简洁的写法，常规的构建一个 pq 优先队列需要自己新建一个类型，然后实现 Len()、Less()、Swap()、Push()、Pop() 这 5 个方法。在 sort 包里有一个现成的最小堆，sort.IntSlice。可以借用它，再自己实现 Push()、Pop()就可以使用最小堆了，节约一部分代码。
+
+## 代码
+
+```go
+package leetcode
+
+import (
+	"container/heap"
+	"sort"
+)
+
+type KthLargest struct {
+	sort.IntSlice
+	k int
+}
+
+func Constructor(k int, nums []int) KthLargest {
+	kl := KthLargest{k: k}
+	for _, val := range nums {
+		kl.Add(val)
+	}
+	return kl
+}
+
+func (kl *KthLargest) Push(v interface{}) {
+	kl.IntSlice = append(kl.IntSlice, v.(int))
+}
+
+func (kl *KthLargest) Pop() interface{} {
+	a := kl.IntSlice
+	v := a[len(a)-1]
+	kl.IntSlice = a[:len(a)-1]
+	return v
+}
+
+func (kl *KthLargest) Add(val int) int {
+	heap.Push(kl, val)
+	if kl.Len() > kl.k {
+		heap.Pop(kl)
+	}
+	return kl.IntSlice[0]
+}
+```