Array

1.Easy

(1). Two Sum

Given an array of integers nums and an integer target, return indices of the two numbers such that they add up to target. You may assume that each input would have exactly one solution, and you may not use the same element twice.假设一组矩阵中只有一组数对作为最终结果

You can return the answer in any order.

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class Solution:
    def two_sum(self, nums, target):
        for i in range(len(nums)):
            for j in range(i+1, len(nums)):
                if nums[j] == target - nums[i]:
                    return [i, j]

(2)Add Two Numbers

(4)Median of Two Sorted Arrays

(26) Remove Element from Sorted Array

Given an integer array nums sorted in non-decreasing order, remove the duplicates in-place such that each unique element appears only once.（巨大前提是数据广义单增） The relative order of the elements should be kept the same. Then return the number of unique elements in nums.

Consider the number of unique elements of nums to be k, to get accepted, you need to do the following things:

Change the array nums such that the first k elements of nums contain the unique elements in the order they were present in nums initially. The remaining elements of nums are not important as well as the size of nums. Return k.

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class Solution(object):
    def removeDuplicates(self, nums):
        dummy=1
        for i in range(1,len(nums)):
            if nums[i]!=nums[i-1]:
                nums[dummy]=nums[i]
                dummy+=1
        return dummy

(27) Remove Elements

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class Solution(object):
    def removeElement(self, nums, val):
        index=0
        for i in range(len(nums)):
            if nums[i]!=val:
                nums[index]=nums[i]
                index+=1
        return index

solution = Solution()
val=3
nums = [3,2,2,3]
result = solution.removeElement(nums,val)
print(result)

(35) Search Insert Position

Method 1：Biscant

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class Solution(object):
    def searchInsert(self, nums, target):
        left=0
        right=len(nums)-1
        
        while left<=right:
            mid=(left+right)//2
            if nums[mid]==target:
                return mid
            elif nums[mid]>target:
                right=mid-1
            else:
                left=mid+1
        return left

Method 2: Traditional Index

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class Solution(object):
    def searchInsert(self, nums, target):
        k=0
        s=0
        for i in range(len(nums)):
            if nums[i]!=target:
                k+=1
            else:
                return k
        for j in range(1,len(nums)):
            if nums[j-1] < target:
                if nums[j] > target:
                    return j
        return(len(nums))

(66) Plus One

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class Solution:
    def plusOne(self, digits) :
        digits = int(''.join(map(str, digits)))
        digits+=1
        digits = [int(digit) for digit in str(digits)]
        return digits

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class Solution:
    def plusOne(self, digits):
        idx=len(digits)-1
        while idx>=0:
            if digits[idx]==9:
                digits[idx]=0
            else:
                digits[idx]+=1
                return digits
            idx -=1
        return digits

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class Solution:
    def plusOne(self, digits): 
        for i, d in reversed(list(enumerate(digits))):
            if d < 9:
                digits[i] += 1
            return digits
            digits[i] = 0

        return [1] + digits

(121)Best Time to Buy and Sell Stock

(136)Single Number

(169)Majority Element

(283)Move Zeroes

(448)Find All Numbers Disappeared in an Array

2.Medium

(15)3Sum

(31)Next Permutation

(33)Search in Rotated Sorted Array

(34)Find First and Last Position of Element in Sorted Array

(53)Maximum Subarray

(55)Jump Game

(56)Merge Intervals

(64)Minimum Path Sum

(79)Word Search

(105)Construct Binary Tree from Preorder and Inorder Traversal

(128)Longest Consecutive Sequence

(139)Word Break

(152)Maximum Product Subarray

(198)House Robber

(200)Number of Islands

(215)Kth Largest Element in an Array

(221)Maximal Square

(238)Product of Array Except Self

(240)Search a 2D Matrix II

(253)Meeting Rooms II

(300)Longest Increasing Subsequence

(309)Best Time to Buy and Sell Stock with Cooldown

(338)Counting Bits

(347)Top K Frequent Elements

(399)Evaluate Division

(406)Queue Reconstruction by Height

(416)Partition Equal Subset Sum

(581)Shortest Unsorted Continuous Subarray

(621)Task Scheduler

(739)Daily Temperatures

3.Hard

(84)Largest Rectangle in Histogram

(85)Maximal Rectangle

(239)Sliding Window Maximum

(312)Burst Balloons