Leetcode Min Stack

標籤：

Design a stack that supports push, pop, top, and retrieving the minimum element in constant time.

• push(x) -- Push element x onto stack.
• pop() -- Removes the element on top of the stack.
• top() -- Get the top element.
• getMin() -- Retrieve the minimum element in the stack.

解題思路：

比較直觀。用一個min stack專門存放最小值，如果有比它小或是相等的（有多個平行的最小值都要單獨存放，否則pop後會出問題），

則存放其到minstack.

Java code:

class MinStack {    Stack<Integer> elements = new Stack<Integer>();      Stack<Integer> minStack = new Stack<Integer>();            public void push(int x) {       elements.push(x);       if(minStack.isEmpty() || x <= minStack.peek()){           minStack.push(x);       }    }    public void pop() {       if(elements.isEmpty()){           return;       }       if((int)elements.peek() == (int)(minStack.peek())){           minStack.pop();       }       elements.pop();    }    public int top() {        return elements.peek();    }    public int getMin() {        return minStack.peek();    }}

Reference:

1. http://www.cnblogs.com/yuzhangcmu/p/4106783.html

 

Leetcode Min Stack