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0155 最小栈.md

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0155 最小栈

Question:

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:

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.

Solution:

class MinStack {
    class Node{
        int value;
        int min;
        Node next;
        public Node(int value,int min){
            this.value=value;
            this.min=min;
            next=null;
        }
    }
    Node top;
    /** initialize your data structure here. */
    public MinStack() {
        top=null;
    }
    
    public void push(int x) {
        if(top==null){
            top=new Node(x,x);
        }else{
            Node another=new Node(x,Math.min(x,getMin()));
            another.next=top;
            top=another;
        }
    }
    
    public void pop() {
        top=top.next;
    }
    
    public int top() {
        return top.value;
    }
    
    public int getMin() {
        return top.min;
    }
}

/**
 * Your MinStack object will be instantiated and called as such:
 * MinStack obj = new MinStack();
 * obj.push(x);
 * obj.pop();
 * int param_3 = obj.top();
 * int param_4 = obj.getMin();
 */