100169. Min Stack LCCI

难度: Easy

题目描述

How would you design a stack which, in addition to push and pop, has a function min which returns the minimum element? Push, pop and min should all operate in 0(1) time.

Example:

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.

解题思路

代码实现

解决方案

java

class MinStack {

    private Stack<Integer> mainStack; // 主栈，存储常规元素
    private Stack<Integer> minStack; // 辅助栈，存储当前最小值

    /** initialize your data structure here. */
    public MinStack() {
        mainStack = new Stack<>();
        minStack = new Stack<>();
    }

    public void push(int x) {
        mainStack.push(x);
        if (minStack.isEmpty()) {
            minStack.push(x);
            return;
        }
        if (minStack.peek() <= x) {
            minStack.push(minStack.peek());
        }else{
             minStack.push(x);
        }

    }

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

    public int top() {
        return mainStack.peek();
    }

    public int getMin() {
        return 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();
 */