Question

面试题 03.05. 栈排序

English Version

题目描述

栈排序。 编写程序，对栈进行排序使最小元素位于栈顶。最多只能使用一个其他的临时栈存放数据，但不得将元素复制到别的数据结构（如数组）中。该栈支持如下操作：push、pop、peek 和 isEmpty。当栈为空时，peek 返回 -1。

示例1:

 输入：
["SortedStack", "push", "push", "peek", "pop", "peek"]
[[], [1], [2], [], [], []]
 输出：
[null,null,null,1,null,2]

示例2:

 输入：
["SortedStack", "pop", "pop", "push", "pop", "isEmpty"]
[[], [], [], [1], [], []]
 输出：
[null,null,null,null,null,true]

说明:

1. 栈中的元素数目在[0, 5000]范围内。

解法

方法一

class SortedStack:
  def __init__(self):
    self.s = []

  def push(self, val: int) -> None:
    t = []
    while not self.isEmpty() and self.s[-1] < val:
      t.append(self.s.pop())
    self.s.append(val)
    while len(t) > 0:
      self.s.append(t.pop())

  def pop(self) -> None:
    if not self.isEmpty():
      self.s.pop()

  def peek(self) -> int:
    return -1 if self.isEmpty() else self.s[-1]

  def isEmpty(self) -> bool:
    return len(self.s) == 0

class SortedStack {
  private Stack<Integer> s;
  public SortedStack() {
    s = new Stack<>();
  }

  public void push(int val) {
    Stack<Integer> t = new Stack<>();
    while (!isEmpty() && s.peek() < val) {
      t.push(s.pop());
    }
    s.push(val);
    while (!t.isEmpty()) {
      s.push(t.pop());
    }
  }

  public void pop() {
    if (!isEmpty()) {
      s.pop();
    }
  }

  public int peek() {
    return isEmpty() ? -1 : s.peek();
  }

  public boolean isEmpty() {
    return s.isEmpty();
  }
}

/**
 * Your SortedStack object will be instantiated and called as such:
 * SortedStack obj = new SortedStack();
 * obj.push(val);
 * obj.pop();
 * int param_3 = obj.peek();
 * boolean param_4 = obj.isEmpty();
 */

type SortedStack struct {
  data []int
}

func Constructor() SortedStack {
  return SortedStack{make([]int, 0)}
}

func (s *SortedStack) Push(val int) {
  temp := make([]int, 0)
  for !s.IsEmpty() && s.Peek() < val {
    temp = append(temp, s.Peek())
    s.Pop()
  }
  s.data = append(s.data, val)
  for len(temp) > 0 {
    s.data = append(s.data, temp[len(temp)-1])
    temp = temp[:len(temp)-1]
  }
}

func (s *SortedStack) Pop() {
  if !s.IsEmpty() {
    s.data = s.data[:len(s.data)-1]
  }
}

func (s *SortedStack) Peek() int {
  if !s.IsEmpty() {
    return s.data[len(s.data)-1]
  }
  return -1
}

func (s *SortedStack) IsEmpty() bool {
  return len(s.data) == 0
}

class SortedStack {
  stack: number[];
  constructor() {
    this.stack = [];
  }

  push(val: number): void {
    let t = [];
    while (!this.isEmpty() && this.peek() < val) {
      t.push(this.stack.pop());
    }
    this.stack.push(val);
    while (t.length > 0) {
      this.stack.push(t.pop());
    }
  }

  pop(): void {
    this.stack.pop();
  }

  peek(): number {
    return this.isEmpty() ? -1 : this.stack[this.stack.length - 1];
  }

  isEmpty(): boolean {
    return this.stack.length == 0;
  }
}

/**
 * Your SortedStack object will be instantiated and called as such:
 * var obj = new SortedStack()
 * obj.push(val)
 * obj.pop()
 * var param_3 = obj.peek()
 * var param_4 = obj.isEmpty()
 */

use std::collections::VecDeque;
struct SortedStack {
  stack: VecDeque<i32>,
}

/**
 * `&self` means the method takes an immutable reference.
 * If you need a mutable reference, change it to `&mut self` instead.
 */
impl SortedStack {
  fn new() -> Self {
    Self { stack: VecDeque::new() }
  }

  fn push(&mut self, val: i32) {
    if self.is_empty() || self.peek() > val {
      self.stack.push_back(val);
      return;
    }
    let t = self.stack.pop_back().unwrap();
    self.push(val);
    self.stack.push_back(t);
  }

  fn pop(&mut self) {
    self.stack.pop_back();
  }

  fn peek(&self) -> i32 {
    *self.stack.back().unwrap_or(&-1)
  }

  fn is_empty(&self) -> bool {
    self.stack.is_empty()
  }
}/**
 * Your SortedStack object will be instantiated and called as such:
 * let obj = SortedStack::new();
 * obj.push(val);
 * obj.pop();
 * let ret_3: i32 = obj.peek();
 * let ret_4: bool = obj.is_empty();
 */

方法二

class SortedStack {
  private stack: number[];

  constructor() {
    this.stack = [];
  }

  push(val: number): void {
    if (this.isEmpty() || this.peek() > val) {
      this.stack.push(val);
      return;
    }

    const tmp = this.stack.pop();
    this.push(val);
    this.stack.push(tmp);
  }

  pop(): void {
    this.stack.pop();
  }

  peek(): number {
    return this.stack[this.stack.length - 1] ?? -1;
  }

  isEmpty(): boolean {
    return this.stack.length === 0;
  }
}

/**
 * Your SortedStack object will be instantiated and called as such:
 * var obj = new SortedStack()
 * obj.push(val)
 * obj.pop()
 * var param_3 = obj.peek()
 * var param_4 = obj.isEmpty()
 */