155. 最小栈

import java.util.ArrayDeque;

class MinStack {

/** initialize your data structure here. */

private final ArrayDeque input;
private final ArrayDeque output;
public MinStack() {
input = new ArrayDeque<>();
output = new ArrayDeque<>();
}

public void push(int x) {
input.push(x);
output.push(Math.min(x, output.isEmpty() ? x : output.peek()));
}

public void pop() {
input.pop();
output.pop();
}

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

public int getMin() {
return output.peek();
}
}