LeetCode 每日一题 2021/7/5-2021/7/11
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
-
-
- 7/5 726. Number of Atoms 原子的数量
- 7/6 1418. Display Table of Food Orders in a Restaurant 点菜展示表
- 7/7 1711. Count Good Meals 大餐计数
- 7/8 930. Binary Subarrays With Sum 和相同的二元子数组
- 7/9 面试题 17.10. 主要元素
- 7/10 981. Time Based Key-Value Store 基于时间的键值存储
- 7/11 274. H-Index H 指数
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7/5 726. Number of Atoms 原子的数量
按情况分析
元素s 元素个数num 当前字符c
1.大写字母
判断c之前是否有元素
如果有放入map
重新设置元素s
2.小写字母
之前必定有大写字母 添加入元素s
3.数字
更新num = num*10+int©
4.前括号
如果c之前有元素 将元素放入map
将之前的map放入stack中
5.后括号
如果c之前有元素 将元素放入map
找到’)‘之后的数值tmpv
使用tmpv更新此时tmp中数值
此时stack[-1]必定是一个’(’ 弹出
继续取stack值
如果是’(’ 重新放入stack 继续往后
如果是map 将此map与当前tmp相加
最后结束循环 同样判断是否还要元素s
def countOfAtoms(formula):
"""
:type formula: str
:rtype: str
"""
from collections import defaultdict
n = len(formula)
stack = []
i = 0
s = ""
num = 0
tmp = defaultdict(int)
while i<n:
c = formula[i]
i +=1
if c>="A" and c<="Z":
if s:
if num ==0:
num = 1
tmp[s]+=num
num = 0
s = c
else:
s = c
num = 0
elif c>="a" and c<="z":
s += c
elif c>="0" and c<="9":
num = num*10 + int(c)
elif c=="(":
if s:
if num ==0:
num = 1
tmp[s]+=num
num = 0
s = ""
stack.append(tmp)
tmp = defaultdict(int)
stack.append("(")
elif c==")":
if s:
if num ==0:
num = 1
tmp[s]+=num
num = 0
s = ""
tmpv = 0
while i<n and formula[i]>="0" and formula[i]<="9":
tmpv = tmpv*10+int(formula[i])
i +=1
if i == n:
break
if not tmpv:
tmpv = 1
for k in tmp.keys():
tmp[k] *= tmpv
stack.pop(-1)
while stack:
sv = stack.pop(-1)
if sv=="(":
stack.append(sv)
break
for k in sv.keys():
tmp[k] += sv[k]
if s:
if num ==0:
num = 1
tmp[s]+=num
key = list(tmp.keys())
key.sort()
ans = ""
for k in key:
ans += k
if tmp[k]>1:
ans += str(tmp[k])
return ans
7/6 1418. Display Table of Food Orders in a Restaurant 点菜展示表
哈希表map
foods,tname set 用来记录所有出现过的桌号和菜名
menu[table] 用来记录table这一桌点的菜
排序 菜名 桌号
依次加入ans中
def displayTable(orders):
"""
:type orders: List[List[str]]
:rtype: List[List[str]]
"""
ans = []
menu = {}
foods = set()
tname = set()
for order in orders:
table,food = order[1],order[2]
tname.add(table)
foods.add(food)
m = menu.get(table,{})
m[food] = m.get(food,0)+1
menu[table]=m
firstline = ["Table"]
foods = list(foods)
foods.sort()
firstline.extend(foods)
ans.append(firstline)
tname = list(tname)
tname.sort(key= lambda x: int(x))
for name in tname:
order = [name]
for food in foods:
if food in menu[name]:
order.append(str(menu[name][food]))
else:
order.append("0")
ans.append(order)
return ans
7/7 1711. Count Good Meals 大餐计数
1.哈希表存储 比较
超时
2.用哈希表存储位置i之前的所有数个数
遍历2的幂 找到能与i位置满足的数
最大数maxn 那么最大的2的幂<2*maxn
def countPairs(deliciousness):
"""
:type deliciousness: List[int]
:rtype: int
"""
mod = 10**9+7
from collections import defaultdict
m = defaultdict(int)
for i in deliciousness:
m[i]+=1
l = list(set(deliciousness))
def check(ans):
return ans&(ans-1)==0
ans = 0
for i in range(len(l)-1):
for j in range(i+1,len(l)):
if check(l[i]+l[j]):
ans += m[l[i]]*m[l[j]]
ans %= mod
for i in range(len(l)):
if check(l[i]*2) and m[l[i]]>1:
ans += m[l[i]]*(m[l[i]]-1)//2
ans %= mod
return ans
def countPairs2(deliciousness):
"""
:type deliciousness: List[int]
:rtype: int
"""
mod = 10**9+7
from collections import defaultdict
m = defaultdict(int)
maxn = max(deliciousness)*2
ans = 0
for num in deliciousness:
s=1
while s<=maxn:
ans += m[s-num]
ans %= mod
s = s<<1
m[num]+=1
return ans
7/8 930. Binary Subarrays With Sum 和相同的二元子数组
前缀和 m用来记录前缀和
def numSubarraysWithSum(nums, goal):
"""
:type nums: List[int]
:type goal: int
:rtype: int
"""
m={}
m[0]=1
s = 0
ans = 0
for num in nums:
s += num
ans += m.get(s-goal,0)
m[s] = m.get(s,0)+1
return(ans)
7/9 面试题 17.10. 主要元素
1.先排序 如果存在出现次数多于一半的数 必定在中间位置
2.摩尔投票 找到出现次数最多的数 再计算它出现的次数是否多于一半
def majorityElement(nums):
"""
:type nums: List[int]
:rtype: int
"""
n=len(nums)
nums.sort()
mid=n//2
l = mid
while l>=0:
if nums[l]==nums[mid]:
l-=1
else:
break
r = mid
while r<n:
if nums[r]==nums[mid]:
r+=1
else:
break
num = r-l-1
return nums[mid] if num>=n//2+1 else -1
def majorityElement2(nums):
"""
:type nums: List[int]
:rtype: int
"""
n=len(nums)
count = 0
curr = -1
for num in nums:
if count==0:
curr = num
count=1
elif curr == num:
count+=1
else:
count-=1
s = 0
print(curr)
for num in nums:
if curr==num:
s+=1
return curr if s>=n//2+1 else -1
7/10 981. Time Based Key-Value Store 基于时间的键值存储
valuemap 用来存储key键下的value
stampmap 用来存储key键下的时间戳
因为set时间戳是递增的 所以stampmap[key] = [xx,xx,xx] 中的list是个严格递增的序列
因此可以使用二分查找找到不大于timestamp的最大值
from collections import defaultdict
class TimeMap(object):
def __init__(self):
"""
Initialize your data structure here.
"""
self.valuemap = defaultdict(list)
self.stampmap = defaultdict(list)
def set(self, key, value, timestamp):
"""
:type key: str
:type value: str
:type timestamp: int
:rtype: None
"""
self.valuemap[key].append(value)
self.stampmap[key].append(timestamp)
def get(self, key, timestamp):
"""
:type key: str
:type timestamp: int
:rtype: str
"""
stamplist = self.stampmap[key]
if not stamplist:
return ""
if timestamp<stamplist[0]:
return ""
if timestamp>=stamplist[-1]:
return self.valuemap[key][-1]
l,r = 0,len(stamplist)-1
print(stamplist)
while l<=r:
mid = (l+r)>>1
print(l,r,mid)
if stamplist[mid]==timestamp:
return self.valuemap[key][mid]
if stamplist[mid]<timestamp:
l = mid+1
else:
r = mid-1
if r>=0:
return self.valuemap[key][r]
return ""
7/11 274. H-Index H 指数
两层二分
最大的可能数 = min(len(citations),max(citations))
check:
二分判断num是否满足h指数条件
二分寻找最大的可能性num
def hIndex(citations):
"""
:type citations: List[int]
:rtype: int
"""
if not citations:
return 0
citations.sort()
n = min(len(citations),max(citations))
def check(num):
l,r = 0,len(citations)-1
while l<=r:
mid = (l+r)>>1
if citations[mid]>=num:
r = mid-1
else:
l = mid+1
if len(citations)-r-1>=num:
return True
return False
l,r = 0,n
ans = 0
while l<=r:
mid = (l+r)>>1
if check(mid):
ans = mid
l = mid+1
else:
r = mid-1
return ans