记录了初步解题思路 以及本地实现代码；并不一定为最优 也希望大家能一起探讨 一起进步
目录
20. valid-parentheses 有效的括号
解题思路：将左边的括号放入栈中 弹出时检查是否一致
def isValid(s):
"""
:type s: str
:rtype: bool
"""
#'(', ')', '{', '}', '[' and ']'
if len(s) % 2 != 0:
return False
l =[]
left =['(','{','[']
for i in s:
if i in left:
l.append(i)
else:
if len(l)==0:
return False
if i==')' and len(l)>0 and l.pop()!='(':
return False
if i=='}' and len(l)>0 and l.pop()!='{':
return False
if i==']' and len(l)>0 and l.pop()!='[':
return False
return l==[]
155.min-stack 最小栈
解题思路：
class MinStack(object):
def __init__(self):
"""
initialize your data structure here.
"""
self.stack = []
self.min = []
def push(self, x):
"""
:type x: int
:rtype: void
"""
self.stack.append(x)
if not self.min or x<=self.min[-1]:
self.min.append(x)
def pop(self):
"""
:rtype: void
"""
v = self.stack.pop()
if self.min and v == self.min[-1]:
self.min.pop()
def top(self):
"""
:rtype: int
"""
if len(self.stack)>0:
return self.stack[-1]
def getMin(self):
"""
:rtype: int
"""
if len(self.min)>0:
return self.min[-1]
225.implement-stack-using-queues 用队列实现栈
解题思路：
class MyStack(object):
def __init__(self):
"""
Initialize your data structure here.
"""
self.stack=[]
def push(self, x):
"""
Push element x onto stack.
:type x: int
:rtype: void
"""
self.stack.append(x)
def pop(self):
"""
Removes the element on top of the stack and returns that element.
:rtype: int
"""
return self.stack.pop()
def top(self):
"""
Get the top element.
:rtype: int
"""
return self.stack[-1]
def empty(self):
"""
Returns whether the stack is empty.
:rtype: bool
"""
return len(self.stack)==0
232.implement-queue-using-stacks 用栈实现队列
解题思路：
class MyQueue(object):
def __init__(self):
"""
Initialize your data structure here.
"""
self.queue=[]
def push(self, x):
"""
Push element x to the back of queue.
:type x: int
:rtype: void
"""
self.queue.append(x)
def pop(self):
"""
Removes the element from in front of queue and returns that element.
:rtype: int
"""
return self.queue.pop(0)
def peek(self):
"""
Get the front element.
:rtype: int
"""
return self.queue[0]
def empty(self):
"""
Returns whether the queue is empty.
:rtype: bool
"""
return len(self.queue)==0
496.next-greater-element-i 下一个更大元素 I
解题思路：
def nextGreaterElement(findNums, nums):
"""
:type findNums: List[int]
:type nums: List[int]
:rtype: List[int]
"""
def find(n,l):
ret = -1
for i in l:
if i >n:
ret = i
return ret
return ret
ret =[]
for i in findNums:
pos = nums.index(i)
ans = find(i,nums[pos+1:])
ret.append(ans)
return ret
682.baseball-game 棒球比赛
解题思路：创建一个list用来储存有效分值
def calPoints(ops):
"""
:type ops: List[str]
:rtype: int
"""
l=[]
sum = 0
for i in ops:
if i=="+":
v = l[-1]+l[-2]
l.append(v)
sum+=v
elif i=="D":
v = 2* l[-1]
l.append(v)
sum+=v
elif i=="C":
v = l.pop()
sum-=v
else:
sum += int(i)
l.append(int(i))
print(sum,l)
return sum
844.backspace-string-compare 比较含退格的字符串
解题思路：
def backspaceCompare(S, T):
"""
:type S: str
:type T: str
:rtype: bool
"""
rs=[]
rt=[]
for i in S:
if i=="#":
if rs:
rs.pop()
else:
rs.append(i)
for i in T:
if i=="#":
if rt:
rt.pop()
else:
rt.append(i)
print(rs,rt)
return rs==rt