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Leetcode155.java
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Leetcode155.java
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package stack;
import java.util.ArrayList;
/**
* @BelongsProject: LeetCode
* @BelongsPackage: com.elvis.leetcode.stack
* @Author: Elvis
* @CreateTime: 2019-03-25 10:59
* Description: MInStack
* 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。
*
* push(x) —— 将元素 x 推入栈中。
* pop() —— 删除栈顶的元素。
* top() —— 获取栈顶元素。
* getMin() —— 检索栈中的最小元素。
*
*
* 示例:
*
* 输入:
* ["MinStack","push","push","push","getMin","pop","top","getMin"]
* [[],[-2],[0],[-3],[],[],[],[]]
*
* 输出:
* [null,null,null,null,-3,null,0,-2]
*
* 解释:
* MinStack minStack = new MinStack();
* minStack.push(-2);
* minStack.push(0);
* minStack.push(-3);
* minStack.getMin(); --> 返回 -3.
* minStack.pop();
* minStack.top(); --> 返回 0.
* minStack.getMin(); --> 返回 -2.
*/
public class Leetcode155 {
/**
* 设计思路 首先使用两个数组list stack min
* stack用来存放栈数据 min用来保存每一次当前的最小值
* 若当前入栈的值x小于上一次的最小值 则将x压入min栈 否则取上一次的最小值压入min栈
* push则直接压入stack栈 对于min栈 若为空则直接入栈 否则判断x与min栈顶元素大小
*/
class MinStack {
ArrayList<Integer> stack;
ArrayList<Integer> min;
/**
* initialize your data structure here.
*/
public MinStack() {
stack = new ArrayList<>();
min = new ArrayList<>();
}
public void push(int x) {
stack.add(x);
int idx = min.size();
if (idx == 0 || min.get(idx - 1) > x) {
min.add(x);
} else {
min.add(min.get(idx - 1));
}
}
public void pop() {
if (stack.size() == 0) throw new RuntimeException("栈为空");
stack.remove(stack.size() - 1);
min.remove(min.size() - 1);
}
public int top() {
if (stack.size() == 0) throw new RuntimeException("栈为空");
return stack.get(stack.size() - 1);
}
public int getMin() {
if (min.size() == 0) throw new RuntimeException("栈为空");
return min.get(min.size() - 1);
}
}
}