leetcode Top 100 Liked Questions Python
这篇文章是关于LeetCode Top 100 Liked Questions 的 专栏记录，其中部分题目可能包括解题思路和多种优化解法。
参考：https://blog.csdn.net/linxid/article/details/88752294
https://blog.csdn.net/lanyu_01/article/details/81062232?utm_medium=distribute.pc_relevant_t0.none-task-blog-BlogCommendFromMachineLearnPai2-1.nonecase&depth_1-utm_source=distribute.pc_relevant_t0.none-task-blog-BlogCommendFromMachineLearnPai2-1.nonecase
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.
Example:
Given nums = [2, 7, 11, 15], target = 9,
Because nums[0] + nums[1] = 2 + 7 = 9,
return [0, 1].
# 此方法需要遍历两边数组
class Solution(object):
# 56ms 93.92%
def twoSum(self, nums, target):
for index in range(len(nums)):
temp = target-nums[index]
if temp in nums_dict and nums.index(temp) != index:
return [index, nums.index(temp)]
# 仅需遍历一遍数组的
class Solution(object):
def twoSum(self, nums, target):
nums_dict = dict()
for index in range(len(nums)):
temp = target-nums[index]
if temp in nums_dict:
return [index,nums_dict[temp]]
nums_dict[nums[index]] = index
2、Add Two Numbers
Description:
You are given two non-empty linked lists representing two non-negative integers. The digits are stored in reverse order and each of their nodes contain a single digit. Add the two numbers and return it as a linked list.
You may assume the two numbers do not contain any leading zero, except the number 0 itself.
Example:
Input: (2 -> 4 -> 3) + (5 -> 6 -> 4)
Output: 7 -> 0 -> 8
Explanation: 342 + 465 = 807.
class ListNode:
def __init__(self, x):
self.val = x
self.next = None
class Solution:
def addTwoNumbers(self, l1: ListNode, l2: ListNode) -> ListNode:
# 官方的解释：此为type hints，是Python 3.5新加的功能。类型建议符并非强制规定和检查，
# 也就是说即使传入的实际参数与建议参数不符，也不会报错。
# 函数参数中的“：”是参数的类型建议符（告诉程序员希望传入的实参的类型）。
# 函数后面跟着的“->”是函数返回值的类型建议符（用来说明该函数返回的值是什么类型）。
prenode = ListNode(0)
lastnode = prenode
val = 0
while val or l1 or l2:
val, cur = divmod(val + (l1.val if l1 else 0) + (l2.val if l2 else 0), 10)
# val, l1.val, l2.val = 0, 1, 9; val, cur = 1, 0
# val, l1.val, l2.val = 1, 5, 1; val, cur = 0, 7
# val, l1.val, l2.val = 0, 8, 2; val, cur = 1, 0
# val, l1.val, l2.val = 0, None, 9; val, cur = 1, 0
# 函数把除数和余数运算结果结合起来，返回一个包含商和余数的元组(a // b, a % b)
lastnode.next = ListNode(cur)
lastnode = lastnode.next
l1 = l1.next if l1 else None
l2 = l2.next if l2 else None
return prenode.next
def generateList(l: list) -> ListNode:
preNode = ListNode(0)
curNode = preNode
for val in l:
curNode.next = ListNode(val)
curNode = curNode.next
return preNode.next
def printList(l: ListNode):
while(l):
print("%d" % l.val, end=', ')
l = l.next
if __name__ == "__main__":
l1 = generateList([1, 5, 8])
l2 = generateList([9, 1, 2, 9])
printList(l1)
printList(l2)
s = Solution()
sum = s.addTwoNumbers(l1, l2)
printList(sum)
3、Longest Substring Without Repeating Characters ~ O(n3)
Description:
Given a string, find the length of the longest substring without repeating characters.
Examples:
Given "abcabcbb", the answer is "abc", which the length is 3.
Given "bbbbb", the answer is "b", with the length of 1.
Given "pwwkew", the answer is "wke", with the length of 3.
class Solution(object):
def lengthOfLongestSubstring(self, s: str) -> int:
# 字符串为空则返回零
if not s:
return 0
window = [] # 滑动窗口数组
max_length = 0 # 最长串长度
# 遍历字符串
for c in s:
# 如果字符不在滑动窗口中，则直接扩展窗口
if c not in window:
# 使用当前字符扩展窗口
window.append(c)
# 如果字符在滑动窗口中，则
# 1. 从窗口中移除重复字符及之前的字符串部分
# 2. 再扩展窗口
else:
# 从窗口中移除重复字符及之前的字符串部分，新字符串即为无重复字符的字符串
window[:] = window[window.index(c) + 1:]
# 扩展窗口
window.append(c)
# 更新最大长度
max_length = max(len(window), max_length)
return max_length if max_length != 0 else len(s)
s = Solution()
strs = 'abcabcbb'
result = s.lengthOfLongestSubstring(strs)
print(result)4. Median of Two Sorted Arrays
Description:
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.
Example :
nums1 = [1, 3]
nums2 = [2]
The median is 2.0
nums1 = [1, 2]
nums2 = [3, 4]
The median is (2 + 3)/2 = 2.5
暴力解法，4ms
class Solution:
def findMedianSortedArrays(self, nums1: List[int], nums2: List[int]) -> float:
nums1.extend(nums2)
length = len(nums1)
nums1 = sorted(nums1)
if len(nums1)%2 == 0:
return (nums1[int(length/2)-1] + nums1[int(length/2)])/2
else:
return nums1[int((length-1)/2)]
5、Longest Palindromic Substring
Description:
Given a string s, find the longest palindromic substring in s. You may assume that the maximum length of s is 1000.
Example 1:
Input: "babad"
Output: "bab"
Input: "cbbd"
Output: "bb"11. Container With Most Water
Description:
Given n non-negative integers a1, a2, …, an , where each represents a point at coordinate (i, ai). n vertical lines are drawn such that the two endpoints of line i is at (i, ai) and (i, 0). Find two lines, which together with x-axis forms a container, such that the container contains the most water.
Note: You may not slant the container and n is at least 2.
The above vertical lines are represented by array [1,8,6,2,5,4,8,3,7]. In this case, the max area of water (blue section) the container can contain is 49.
Example:
Input: [1,8,6,2,5,4,8,3,7]
Output: 4915. 3Sum
Description:
Given an array nums of n integers, are there elements a, b, c in nums such that a + b + c = 0? Find all unique triplets in the array which gives the sum of zero.
Note:
The solution set must not contain duplicate triplets.
Example:
Given array nums = [-1, 0, 1, 2, -1, -4],
A solution set is:
[
[-1, 0, 1],
[-1, -1, 2]
]
16. 3Sum Closest
Description:
Given an array nums of n integers and an integer target, find three integers in nums such that the sum is closest to target. Return the sum of the three integers. You may assume that each input would have exactly one solution.
Example:
Given array nums = [-1, 2, 1, -4], and target = 1.
The sum that is closest to the target is 2. (-1 + 2 + 1 = 2).17. Letter Combinations of a Phone Number
Description:
Given a string containing digits from 2-9 inclusive, return all possible letter combinations that the number could represent.
A mapping of digit to letters (just like on the telephone buttons) is given below. Note that 1 does not map to any letters.
Example:
Input: "23"
Output: ["ad", "ae", "af", "bd", "be", "bf", "cd", "ce", "cf"].19. Remove Nth Node From End of List
Description:
Given a linked list, remove the n-th node from the end of list and return its head.
Example:
Given linked list: 1->2->3->4->5, and n = 2.
After removing the second node from the end, the linked list becomes 1->2->3->5.
20. Valid Parentheses
Description:
Given a string containing just the characters ‘(‘, ‘)’, ‘{‘, ‘}’, ‘[’ and ‘]’, determine if the input string is valid.
An input string is valid if:
Open brackets must be closed by the same type of brackets.
Open brackets must be closed in the correct order.
Note that an empty string is also considered valid.
Example 1:
Input: "()"
Output: true
Input: "()[]{}"
Output: true
Input: "(]"
Output: false
Input: "([)]"
Output: false
Input: "{[]}"
Output: true
21. Merge Two Sorted Lists
Description:
Merge two sorted linked lists and return it as a new list. The new list should be made by splicing together the nodes of the first two lists.
Example:
Input: 1->2->4, 1->3->4
Output: 1->1->2->3->4->422. Generate Parentheses
Description:
Given n pairs of parentheses, write a function to generate all combinations of well-formed parentheses.
For example, given n = 3, a solution set is:
[
"((()))",
"(()())",
"(())()",
"()(())",
"()()()"
]23. Merge k Sorted Lists
Description:
Merge k sorted linked lists and return it as one sorted list. Analyze and describe its complexity.
Example:
Input:
[
1->4->5,
1->3->4,
2->6
]
Output: 1->1->2->3->4->4->5->632. Longest Valid Parentheses
Description:
Given a string containing just the characters ‘(’ and ‘)’, find the length of the longest valid (well-formed) parentheses substring.
Example 1:
Input: "(()"
Output: 2
Explanation: The longest valid parentheses substring is "()"
Input: ")()())"
Output: 4
Explanation: The longest valid parentheses substring is "()()"33. Search in Rotated Sorted Array
Description:
Suppose an array sorted in ascending order is rotated at some pivot unknown to you beforehand.
(i.e., [0,1,2,4,5,6,7] might become [4,5,6,7,0,1,2]).
You are given a target value to search. If found in the array return its index, otherwise return -1.
You may assume no duplicate exists in the array.
Your algorithm’s runtime complexity must be in the order of O(log n).
Example 1:
Input: nums = [4,5,6,7,0,1,2], target = 0
Output: 4
Input: nums = [4,5,6,7,0,1,2], target = 3
Output: -134. Find First and Last Position of Element in Sorted Array
Description:
Given an array of integers nums sorted in ascending order, find the starting and ending position of a given target value.
Your algorithm’s runtime complexity must be in the order of O(log n).
If the target is not found in the array, return [-1, -1].
Example 1:
Input: nums = [5,7,7,8,8,10], target = 8
Output: [3,4]
Input: nums = [5,7,7,8,8,10], target = 6
Output: [-1,-1]35. Search Insert Position
Description:
Given a sorted array and a target value, return the index if the target is found. If not, return the index where it would be if it were inserted in order.
You may assume no duplicates in the array.
Example 1:
Input: [1,3,5,6], 5
Output: 2
Input: [1,3,5,6], 2
Output: 1
Input: [1,3,5,6], 7
Output: 4
Input: [1,3,5,6], 0
Output: 039. Combination Sum
Description:
Given a set of candidate numbers (candidates) (without duplicates) and a target number (target), find all unique combinations in candidates where the candidate numbers sums to target.
The same repeated number may be chosen from candidates unlimited number of times.
Note:
All numbers (including target) will be positive integers.
The solution set must not contain duplicate combinations.
Example 1:
Input: candidates = [2,3,6,7], target = 7,
A solution set is:
[
[7],
[2,2,3]
]
Input: candidates = [2,3,5], target = 8,
A solution set is:
[
[2,2,2,2],
[2,3,3],
[3,5]
]42. Trapping Rain Water
Description:
Given n non-negative integers representing an elevation map where the width of each bar is 1, compute how much water it is able to trap after raining.
The above elevation map is represented by array [0,1,0,2,1,0,1,3,2,1,2,1]. In this case, 6 units of rain water (blue section) are being trapped. Thanks Marcos for contributing this image!
Example:
Input: [0,1,0,2,1,0,1,3,2,1,2,1]
Output: 646. Permutations
Description:
Given a collection of distinct integers, return all possible permutations.
Example:
Input: [1,2,3]
Output:
[
[1,2,3],
[1,3,2],
[2,1,3],
[2,3,1],
[3,1,2],
[3,2,1]
]48. Rotate Image
Description:
You are given an n x n 2D matrix representing an image.
Rotate the image by 90 degrees (clockwise).
Note:
You have to rotate the image in-place, which means you have to modify the input 2D matrix directly. DO NOT allocate another 2D matrix and do the rotation.
Example 1:
Given input matrix =
[
[1,2,3],
[4,5,6],
[7,8,9]
],
rotate the input matrix in-place such that it becomes:
[
[7,4,1],
[8,5,2],
[9,6,3]
]
Given input matrix =
[
[ 5, 1, 9,11],
[ 2, 4, 8,10],
[13, 3, 6, 7],
[15,14,12,16]
],
rotate the input matrix in-place such that it becomes:
[
[15,13, 2, 5],
[14, 3, 4, 1],
[12, 6, 8, 9],
[16, 7,10,11]
]49. Group Anagrams
Description:
Given an array of strings, group anagrams together.
Example:
Input: ["eat", "tea", "tan", "ate", "nat", "bat"],
Output:
[
["ate","eat","tea"],
["nat","tan"],
["bat"]
]
Note:
All inputs will be in lowercase.
The order of your output does not matter.53. Maximum Subarray
Description:
Given an integer array nums, find the contiguous subarray (containing at least one number) which has the largest sum and return its sum.
Example:
Input: [-2,1,-3,4,-1,2,1,-5,4],
Output: 6
Explanation: [4,-1,2,1] has the largest sum = 6.55. Jump Game
Description:
Given an array of non-negative integers, you are initially positioned at the first index of the array.
Each element in the array represents your maximum jump length at that position.
Determine if you are able to reach the last index.
Example 1:
Input: [2,3,1,1,4]
Output: true
Explanation: Jump 1 step from index 0 to 1, then 3 steps to the last index.
Input: [3,2,1,0,4]
Output: false
Explanation: You will always arrive at index 3 no matter what. Its maximum
jump length is 0, which makes it impossible to reach the last index.56. Merge Intervals
Description:
Given a collection of intervals, merge all overlapping intervals.
Example 1:
Input: [[1,3],[2,6],[8,10],[15,18]]
Output: [[1,6],[8,10],[15,18]]
Explanation: Since intervals [1,3] and [2,6] overlaps, merge them into [1,6].
Input: [[1,4],[4,5]]
Output: [[1,5]]
Explanation: Intervals [1,4] and [4,5] are considerred overlapping.