🌗 155. 最小栈

难度: 🌗

问题描述

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解法

class MinStack {
    // 思路：
    // 2 个栈，一个栈进行常规操作，另一个栈存放非严格单调递减数
    LinkedList<Integer> stack;
    LinkedList<Integer> minS;

    public MinStack() {
        this.stack = new LinkedList<>();
        this.minS = new LinkedList<>();
    }
    
    public void push(int val) {
        stack.push(val);
        if(minS.isEmpty() || val <= minS.peek()) {
            minS.push(val);
        }
    }
    
    public void pop() {
        int val = stack.pop();
        if(!minS.isEmpty() && val == minS.peek()) {
            minS.pop();
        }
    }
    
    public int top() {
        if(stack.isEmpty()) {
            return -1;
        } else {
            return stack.peek();
        }
    }
    
    public int getMin() {
        if(minS.isEmpty()) {
            return -1;
        } else {
            return minS.peek();
        }
    }
}

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

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输出