## Solutions
### first try
```python
class MinStack(object):
def __init__(self):
self.stack = []
def push(self, val):
"""
:type val: int
:rtype: None
"""
self.stack.append(val)
def pop(self):
"""
:rtype: None
"""
self.stack.pop()
def top(self):
"""
:rtype: int
"""
return self.stack[-1]
def getMin(self):
"""
:rtype: int
"""
min = self.top()
for element in self.stack:
if element < min:
min = element
return min
# Your MinStack object will be instantiated and called as such:
# obj = MinStack()
# obj.push(val)
# obj.pop()
# param_3 = obj.top()
# param_4 = obj.getMin()
```
- Complexity Analysis
- Time complexity is On because we use for loop in getMin
- Space complexity is
### 优化 getMin
```python
class MinStack(object):
def __init__(self):
self.stack = []
self.min_stack = []
def push(self, val):
"""
:type val: int
:rtype: None
"""
self.stack.append(val)
if not self.min_stack or val < self.min_stack[-1]:
self.min_stack.append(val)
else:
self.min_stack.append(self.min_stack[-1])
def pop(self):
"""
:rtype: None
"""
self.stack.pop()
self.min_stack.pop()
def top(self):
"""
:rtype: int
"""
return self.stack[-1]
def getMin(self):
"""
:rtype: int
"""
if self.min_stack:
return self.min_stack[-1]
# Your MinStack object will be instantiated and called as such:
# obj = MinStack()
# obj.push(val)
# obj.pop()
# param_3 = obj.top()
# param_4 = obj.getMin()
```
core idea:
maintain a synchronized `min_stack`, push the smallest value inside each operation, so we can get the min value directly