MinStack.java

package basic.QueueAndStack;

import java.util.Stack;

/**
 * 你实现的栈将支持push，pop 和 min 操作，所有操作要求都在O(1)时间内完成。
 */
public class MinStack {
    public static void main(String[] args) {
        MinStack minStack = new MinStack();
        minStack.push(-2);
        minStack.push(0);
        minStack.push(-3);
        minStack.getMin(); // return -3
        minStack.pop();
        minStack.top();    // return 0
        minStack.getMin(); // return -2
    }

    private Stack<Integer> stack = new Stack();
    private Stack<Integer> minStack = new Stack();

    /**
     * initialize your data structure here.
     */
    public MinStack() {

    }

    public void push(int x) {
        stack.push(x);
        if (minStack.isEmpty() || minStack.peek() >= x) {
            minStack.push(x);
        } else {
            minStack.push(minStack.peek());
        }
    }

    public void pop() {
        minStack.pop();
        stack.pop();
    }

    public int top() {
        return stack.isEmpty() ? 0 : stack.peek();
    }

    public int getMin() {
        return stack.isEmpty() ? 0 : minStack.peek();
    }
}

/**
 * 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();
 */