155 Min Stack 最小栈
Description:
Design a stack that supports push, pop, top, and retrieving the minimum element in constant time.
push(x) -- Push element x onto stack.
pop() -- Removes the element on top of the stack.
top() -- Get the top element.
getMin() -- Retrieve the minimum element in the stack.
Example:
Example 1:
MinStack minStack = new MinStack();
minStack.push(-2);
minStack.push(0);
minStack.push(-3);
minStack.getMin(); --> Returns -3.
minStack.pop();
minStack.top(); --> Returns 0.
minStack.getMin(); --> Returns -2.
题目描述:
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:
栈可以用数组实现或者链表实现
- 用一个栈记录最小值
- 将最小值直接记录在这个栈
如, 输入 -2 -> 0 -> -3, 栈中的记录依次为 -2 -> -2 -> 0 -> -2 -> -3 -> -3
获取最小值直接返回最后一项即可
空间换时间
时间复杂度O(1), 空间复杂度O(n)
代码:
C++:
class MinStack
{
public:
/** initialize your data structure here. */
vector<int> data;
MinStack() {}
void push(int x)
{
if (data.empty()) data.push_back(x);
else data.push_back(min(x, data[data.size() - 2]));
data.push_back(x);
}
void pop()
{
data.pop_back();
data.pop_back();
}
int top()
{
return data.back();
}
int getMin()
{
return data[data.size() - 2];
}
};
/**
* 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();
*/
Java:
class MinStack {
/** initialize your data structure here. */
private List<Integer> list;
public MinStack() {
list = new ArrayList<>();
}
public void push(int x) {
if (list.isEmpty()) list.add(x);
else list.add(Math.min(x, list.get(list.size() - 2)));
list.add(x);
}
public void pop() {
list.remove(list.size() - 1);
list.remove(list.size() - 1);
}
public int top() {
if (list.size() != 0) return list.get(list.size() - 1);
return 0;
}
public int getMin() {
if (list.size() != 0) return list.get(list.size() - 2);
return 0;
}
}
/**
* 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();
*/
Python:
class MinStack:
def __init__(self):
"""
initialize your data structure here.
"""
self.data = []
def push(self, x: int) -> None:
if not self.data:
self.data.append(x)
else:
self.data.append(min(self.data[-2], x))
self.data.append(x)
def pop(self) -> None:
self.data.pop()
self.data.pop()
def top(self) -> int:
if self.data:
return self.data[-1]
def getMin(self) -> int:
if self.data:
return self.data[-2]
# Your MinStack object will be instantiated and called as such:
# obj = MinStack()
# obj.push(x)
# obj.pop()
# param_3 = obj.top()
# param_4 = obj.getMin()
