最小栈
设计一个支持 push
,pop
,top
操作,并能在常数时间内检索到最小元素的栈。
push(x)
—— 将元素 x 推入栈中。pop()
—— 删除栈顶的元素。top()
—— 获取栈顶元素。getMin()
—— 检索栈中的最小元素。
示例:
MinStack minStack = new MinStack();
minStack.push(-2);
minStack.push(0);
minStack.push(-3);
minStack.getMin(); --> 返回 -3.
minStack.pop();
minStack.top(); --> 返回 0.
minStack.getMin(); --> 返回 -2.
思路
一个栈存储所有值,另一个栈存储最小值。
当push
值时,如果最小栈为空或者当前值比最小栈值小,则push
进最小栈。
出栈时,将出栈的值与最小栈里顶上的值比较,一样则一起出栈
解答
import java.util.Stack;
class MinStack {
private Stack<Integer> stack;
private Stack<Integer> minStack;
/** initialize your data structure here. */
public MinStack() {
stack = new Stack<>();
minStack = new Stack<>();
}
public void push(int x) {
stack.push(x);
if (minStack.isEmpty() || x <= minStack.peek())
minStack.push(x);
}
public void pop() {
int top = stack.peek();
stack.pop();
if (top == minStack.peek())
minStack.pop();
}
public int top() {
return stack.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();
*/