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算法题目---------------01.实现一个特殊的栈,在栈的基本功能上,在实现返回栈中最小的元素

程序员文章站 2022-06-08 18:17:55
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要求:

  1. pop,push,getMin操作时间复杂度为O(1)
  2. 设计的栈类型可以使用现成的栈结构

算法题目---------------01.实现一个特殊的栈,在栈的基本功能上,在实现返回栈中最小的元素

设计两个栈,data中不用管,只需要入栈,当data中入栈,则min中做比较,

  • 如果min中没有,则直接入栈,
  • 若有则用min中的栈顶的元素和data中入栈的元素进行比较,
  • 若min中栈顶比较小,则向min中压入当前min栈顶中的元素,若min栈顶中的元素比较大,则压入data中刚刚入栈的元素,当执行弹出的时候,同步弹出即可
public static class MyStack1 {
		private Stack<Integer> stackData;
		private Stack<Integer> stackMin;

		public MyStack1() {
			this.stackData = new Stack<Integer>();
			this.stackMin = new Stack<Integer>();
		}

		public void push(int newNum) {
			if (this.stackMin.isEmpty()) {
				this.stackMin.push(newNum);
			} else if (newNum <= this.getmin()) {
				this.stackMin.push(newNum);
			}
			this.stackData.push(newNum);
		}

		public int pop() {
			if (this.stackData.isEmpty()) {
				throw new RuntimeException("Your stack is empty.");
			}
			int value = this.stackData.pop();
			if (value == this.getmin()) {
				this.stackMin.pop();
			}
			return value;
		}

		public int getmin() {
			if (this.stackMin.isEmpty()) {
				throw new RuntimeException("Your stack is empty.");
			}
			return this.stackMin.peek();
		}
	}

	public static class MyStack2 {
		private Stack<Integer> stackData;
		private Stack<Integer> stackMin;

		public MyStack2() {
			this.stackData = new Stack<Integer>();
			this.stackMin = new Stack<Integer>();
		}

		public void push(int newNum) {
			if (this.stackMin.isEmpty()) {
				this.stackMin.push(newNum);
			} else if (newNum < this.getmin()) {
				this.stackMin.push(newNum);
			} else {
				int newMin = this.stackMin.peek();
				this.stackMin.push(newMin);
			}
			this.stackData.push(newNum);
		}

		public int pop() {
			if (this.stackData.isEmpty()) {
				throw new RuntimeException("Your stack is empty.");
			}
			this.stackMin.pop();
			return this.stackData.pop();
		}

		public int getmin() {
			if (this.stackMin.isEmpty()) {
				throw new RuntimeException("Your stack is empty.");
			}
			return this.stackMin.peek();
		}
	}

	public static void main(String[] args) {
		MyStack1 stack1 = new MyStack1();
		stack1.push(3);
		System.out.println(stack1.getmin());
		stack1.push(4);
		System.out.println(stack1.getmin());
		stack1.push(1);
		System.out.println(stack1.getmin());
		System.out.println(stack1.pop());
		System.out.println(stack1.getmin());

		System.out.println("=============");

		MyStack1 stack2 = new MyStack1();
		stack2.push(3);
		System.out.println(stack2.getmin());
		stack2.push(4);
		System.out.println(stack2.getmin());
		stack2.push(1);
		System.out.println(stack2.getmin());
		System.out.println(stack2.pop());
		System.out.println(stack2.getmin());
	}