MinStack1.java

/**
 * <p>设计一个支持 <code>push</code> ，<code>pop</code> ，<code>top</code> 操作，并能在常数时间内检索到最小元素的栈。</p>
 *
 * <ul>
 * <li><code>push(x)</code> &mdash;&mdash; 将元素 x 推入栈中。</li>
 * <li><code>pop()</code>&nbsp;&mdash;&mdash; 删除栈顶的元素。</li>
 * <li><code>top()</code>&nbsp;&mdash;&mdash; 获取栈顶元素。</li>
 * <li><code>getMin()</code> &mdash;&mdash; 检索栈中的最小元素。</li>
 * </ul>
 *
 * <p>&nbsp;</p>
 *
 * <p><strong>示例:</strong></p>
 *
 * <pre><strong>输入：</strong>
 * [&quot;MinStack&quot;,&quot;push&quot;,&quot;push&quot;,&quot;push&quot;,&quot;getMin&quot;,&quot;pop&quot;,&quot;top&quot;,&quot;getMin&quot;]
 * [[],[-2],[0],[-3],[],[],[],[]]
 *
 * <strong>输出：</strong>
 * [null,null,null,null,-3,null,0,-2]
 *
 * <strong>解释：</strong>
 * MinStack minStack = new MinStack();
 * minStack.push(-2);
 * minStack.push(0);
 * minStack.push(-3);
 * minStack.getMin();   --&gt; 返回 -3.
 * minStack.pop();
 * minStack.top();      --&gt; 返回 0.
 * minStack.getMin();   --&gt; 返回 -2.
 * </pre>
 *
 * <p>&nbsp;</p>
 *
 * <p><strong>提示：</strong></p>
 *
 * <ul>
 * <li><code>pop</code>、<code>top</code> 和 <code>getMin</code> 操作总是在 <strong>非空栈</strong> 上调用。</li>
 * </ul>
 * <div><div>Related Topics</div><div><li>栈</li><li>设计</li></div></div><br><div><li>👍 1081</li><li>👎 0</li></div>
 */

package leetcode1;

import java.util.ArrayDeque;

public class MinStack1 {

    public static void main(String[] args) {
    }

    class MinStack {

        private ArrayDeque<Integer> stack = new ArrayDeque<>();
        private ArrayDeque<Integer> min = new ArrayDeque<>();

        public MinStack() {
        }

        public void push(int val) {
            stack.push(val);
            if (min.isEmpty() || min.peek() >= val) {
                min.push(val);
            }
        }

        public void pop() {
            if (!stack.isEmpty() && stack.pop().equals(min.peek())) {
                min.pop();
            }
        }

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

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

}