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1 | 1 | package com.mistray.stack; |
2 | 2 |
|
| 3 | +import java.util.Stack; |
| 4 | + |
3 | 5 | /** |
4 | 6 | * @author ZJY(MistRay) |
5 | 7 | * @Project algorithm-study |
6 | 8 | * @Package com.mistray.stack |
7 | 9 | * @create 2020年05月21日 14:33 |
8 | 10 | * @Desc |
| 11 | + * 设计一个支持 push ,pop ,top 操作,并能在常数时间内检索到最小元素的栈。 |
| 12 | + * |
| 13 | + * push(x) —— 将元素 x 推入栈中。 |
| 14 | + * pop() —— 删除栈顶的元素。 |
| 15 | + * top() —— 获取栈顶元素。 |
| 16 | + * getMin() —— 检索栈中的最小元素。 |
| 17 | + * |
| 18 | + * |
| 19 | + * 示例: |
| 20 | + * |
| 21 | + * 输入: |
| 22 | + * ["MinStack","push","push","push","getMin","pop","top","getMin"] |
| 23 | + * [[],[-2],[0],[-3],[],[],[],[]] |
| 24 | + * |
| 25 | + * 输出: |
| 26 | + * [null,null,null,null,-3,null,0,-2] |
| 27 | + * |
| 28 | + * 解释: |
| 29 | + * MinStack minStack = new MinStack(); |
| 30 | + * minStack.push(-2); |
| 31 | + * minStack.push(0); |
| 32 | + * minStack.push(-3); |
| 33 | + * minStack.getMin(); --> 返回 -3. |
| 34 | + * minStack.pop(); |
| 35 | + * minStack.top(); --> 返回 0. |
| 36 | + * minStack.getMin(); --> 返回 -2. |
| 37 | + * |
| 38 | + * |
| 39 | + * 提示: |
| 40 | + * |
| 41 | + * pop、top 和 getMin 操作总是在 非空栈 上调用。 |
| 42 | + * |
9 | 43 | */ |
10 | 44 | public class MinStack155 { |
11 | 45 |
|
| 46 | + private Stack<Integer> dataStack; |
| 47 | + private Stack<Integer> minStack; |
| 48 | + |
| 49 | + // 思路: |
| 50 | + // 使用辅助栈的方式,让取最小值的时间复杂度保持在O(1) |
| 51 | + /** initialize your data structure here. */ |
| 52 | + public MinStack155() { |
| 53 | + dataStack = new Stack<>(); |
| 54 | + minStack = new Stack<>(); |
| 55 | + } |
| 56 | + |
| 57 | + public void push(int x) { |
| 58 | + dataStack.push(x); |
| 59 | + if (minStack.isEmpty() || minStack.peek() >= x){ |
| 60 | + minStack.push(x); |
| 61 | + } |
| 62 | + } |
| 63 | + |
| 64 | + public void pop() { |
| 65 | + if (dataStack.pop().equals(minStack.peek()) && minStack.size() > 1){ |
| 66 | + minStack.pop(); |
| 67 | + } |
| 68 | + } |
| 69 | + |
| 70 | + public int top() { |
| 71 | + return dataStack.peek(); |
| 72 | + } |
12 | 73 |
|
| 74 | + public int getMin() { |
| 75 | + return minStack.peek(); |
| 76 | + } |
13 | 77 | } |
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