笔者也是菜鸟一枚,仅要求把题目做出,对算法的优化没有能力做太多处理,希望大家给出改进意见.
1. Two Sum
Given an array of integers, return indices of the two numbers such that they add up to a specific target.
You may assume that each input would have exactly one solution, and you may not use the same element twice.
class Solution:
def twoSum(self, nums, target):
for idx, a in enumerate(nums):
for idx2 in range(idx+1,len(nums)):
if a + nums[idx2] == target :
return [idx,idx2]
Runtime: 4916 ms, faster than 21.56% of Python3 online submissions for Two Sum.
Memory Usage: 13.5 MB, less than 51.57% of Python3 online submissions for Two Sum
3. Longest Substring Without Repeating Characters
Given a string, find the length of the longest substring without repeating characters
class Solution:
def lengthOfLongestSubstring(self, s):
maxnum = 0
for i in range(len(s)):
ss = []
for j in range(i,len(s)):
if (s[j] not in ss):
ss.append(s[j])
if (len(ss))>maxnum :
maxnum = len(ss)
else:
break
return maxnum
这个结果不是很好…
Runtime: 1884 ms, faster than 5.01% of Python3 online submissions for Longest Substring Without Repeating Characters.
Memory Usage: 13.5 MB, less than 5.05% of Python3 online submissions for Longest Substring Without Repeating Characters.
4. Median of Two Sorted Arrays
There are two sorted arrays nums1 and nums2 of size m and n respectively.
Find the median of the two sorted arrays. The overall run time complexity should be O(log (m+n)).
You may assume nums1 and nums2 cannot be both empty.
class Solution:
def findMedianSortedArrays(self, nums1, nums2):
nums = nums1 + nums2
nums.sort()
a = len(nums)
if a % 2 == 1 : return nums[int(a/2)]
else : return 0.5*(nums[int(a/2)] + nums[int(a/2)-1])
Runtime: 56 ms, faster than 100.00% of Python3 online submissions for Median of Two Sorted Arrays.
Memory Usage: 13.6 MB, less than 5.11% of Python3 online submissions for Median of Two Sorted Arrays.
5.Longest Palindromic Substring
Given a string s, find the longest palindromic substring in s. You may assume that the maximum length of s is 1000.
class Solution:
def longestPalindrome(self, s):
if len(s) == 0 : return ""
else:
for j in range(len(s)):
num = len(s)-j
for i in range(j+1):
if s[i] == s[i+num-1]:
if s[i+1:i+num-1] == s[i+num-2:i:-1]:
return(s[i:i+num])
Runtime: 1324 ms, faster than 50.74% of Python3 online submissions for Longest Palindromic Substring.
Memory Usage: 13.2 MB, less than 25.10% of Python3 online submissions for Longest Palindromic Substring.
6.ZigZag Conversion
The string “PAYPALISHIRING” is written in a zigzag pattern on a given number of rows like this: (you may want to display this pattern in a fixed font for better legibility)
P A H N
A P L S I I G
Y I R
And then read line by line: “PAHNAPLSIIGYIR”
Write the code that will take a string and make this conversion given a number of rows:
string convert(string s, int numRows);
class Solution:
def convert(self, s,numRows):
if numRows==1: return s
myresult = ''
a = lambda x : s[x] if 0<=x and x<len(s) else ''
result = ['']*numRows
for i in range(0,len(s)+2*(numRows-1),2*(numRows-1)):
result[0] = result[0] + a(i)
for num in range(1,numRows):
if num < numRows-1:
result[num] = result[num] + a(i-num) + a(i+num)
else :
result[num] = result[num] + a(i+num)
for i in range(numRows):
myresult += result[i]
return myresult
Runtime: 108 ms, faster than 34.63% of Python3 online submissions for ZigZag Conversion.
Memory Usage: 13.3 MB, less than 10.35% of Python3 online submissions for ZigZag Conversion.
7. Reverse Integer
Given a 32-bit signed integer, reverse digits of an integer.
这里注意32-bit signed integer的范围.
class Solution:
def reverse(self, x):
if (x<-2147483648) or (x > 2147483647): return 0
sign = 1
result = 0
if x<0:
x = -x
sign = -1
while x != 0:
result = result*10 + (x%10)
x = int(x/10)
if (result<-2147483648) or (result > 2147483647): return 0
else : return sign*result
Runtime: 40 ms, faster than 99.98% of Python3 online submissions for Reverse Integer.
Memory Usage: 13.2 MB, less than 5.71% of Python3 online submissions for Reverse Integer.
8.
The string can contain additional characters after those that form the integral number, which are ignored and have no effect on the behavior of this function.
If the first sequence of non-whitespace characters in str is not a valid integral number, or if no such sequence exists because either str is empty or it contains only whitespace characters, no conversion is performed.
If no valid conversion could be performed, a zero value is returned.
Note:
Only the space character ’ ’ is considered as whitespace character.
Assume we are dealing with an environment which could only store integers within the 32-bit signed integer range: [−231, 231 − 1]. If the numerical value is out of the range of representable values, INT_MAX (231 − 1) or INT_MIN (−231) is returned.
class Solution:
def myAtoi(self, mystr):
mystr = mystr.lstrip() #去掉头上的空格
if mystr == '': return 0
sign = 1
result = 0
i = 0
if mystr[i] == '-':
sign = -1
i = i + 1
elif mystr[i] == '+': i = i + 1
if i < len(mystr):
while((mystr[i]<='9') & (mystr[i]>='0')):
result = 10*(result) + int(mystr[i])
i +=1
if i == len(mystr): break
result *= sign
if result>2**31-1: return 2**31-1
elif result<-2**31: return -2**31
else: return result
Runtime: 44 ms, faster than 99.93% of Python3 online submissions for String to Integer (atoi).
Memory Usage: 13.4 MB, less than 5.00% of Python3 online submissions for String to Integer (atoi).
9.
Determine whether an integer is a palindrome. An integer is a palindrome when it reads the same backward as forward.
class Solution:
def isPalindrome(y,x):
if x < 0 :
return False
elif x == 0 :
return True
else:
num = []
while(x!=0):
num.append(x % 10)
x= int(x/10)
for i in range(int(len(num)/2)+1):
if num[i] != num[len(num)-1-i]:
return False
return True
Runtime: 140 ms, faster than 85.74% of Python3 online submissions for Palindrome Number.
Memory Usage: 13.3 MB, less than 5.03% of Python3 online submissions for Palindrome Number.
每天做一道更新一道，请大家多批评指教！