문제 난이도 : Easy

문제 유형 : Data Structures - Stack

문제 설명 간략 :

push, pop, top 그리고 최소값을 반환하는 stack을 구현하라.

제약사항

• -2^31 <= val <= 2^31 - 1
• Methods pop, top and getMin operations will always be called on non-empty stacks.
• At most 3 * 10^4 calls will be made to push, pop, top, and getMin.

자바 풀이

class MinStack {

    List<Integer> data = null;

    /** initialize your data structure here. */
    public MinStack() {
        data = new ArrayList<Integer>();
    }

    public void push(int val) {
        data.add(val);
    }

    public void pop() {
        if(data.size() > 0) {
            data.remove(data.size()-1);
        }
    }

    public int top() {
        return data.get(data.size()-1);
    }

    public int getMin() {
        int min = Integer.MAX_VALUE;
        for(int i = 0; i < data.size(); i++) {
            int val = data.get(i);
            if(val  < min) {
                min = val;
            }
        }

        return min;
    }
}

/**
 * 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();
 */

출처

해커랭크 문제