[C language questions -- leetcode 12 questions] take you off and fly into the garbage

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In a word ： In the past , All is prologue

explain : The past is irreparable , The future can change

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Brush the topic ——Leetcode12 A simple question , Through this 12 A simple question , Make you right Leetcode New understanding , Enhance your ability to do questions .

below , Go straight to our topic .

260. A number that appears only once III( difficulty ： secondary )

Given an array of integers nums, There are exactly two elements that only appear once , All the other elements appear twice . Find the two elements that only appear once . You can press In any order Return to the answer .

Advanced ： Your algorithm should have linear time complexity . Can you just use constant space complexity to achieve ？

Example 1：

Input ：nums = [1,2,1,3,2,5]
Output ：[3,5]
explain ：[5, 3] It's also a valid answer .
Example 2：

Input ：nums = [-1,0]
Output ：[-1,0]
Example 3：

Input ：nums = [0,1]
Output ：[1,0]

source ： Power button （LeetCode）

This question Leetcode The difficulty is classified as medium , But I think we can still do it （bushi）：

For the convenience of explanation, the variables here use the names I named in the process of doing the questions

Their thinking ： First , We define a variable （eor） Initialize to 0 To traverse all the elements in a bitwise XOR array , At this point, we get the binary XOR result of two elements that only appear once . And then to process the binary results ： For two different numbers , The binary result of XOR is 1 The words of ： The number in this binary bit is different （ We can define a variable rightone To find the rightmost bit in the binary result at this time 1 The location of , As for how to find it, just look at the code , I'm not going to explain it here ）. Based on this , We are dividing the elements of an array into two categories ： One is the same element in the binary bit , The other is the element that is different in the binary bit . And then we're going through the array once ,& Bitwise AND rightone Find one of the numbers onlyone, As for the other number, it is directly based on the result of the first exclusive or of two numbers eor On XOR onlyone It can be concluded that .

below , Look at our code ：

( reminder ： If the variable here is defined as int Type words , An overflow error will occur , Don't ask me why I know , Because at the beginning, my own is int type , So instead of long The type is appropriate )

Now proceed to submit and run ：

728. Self divisor

Self divisor It refers to the number that can be divided by every digit it contains .

for example ,128 It's a Self divisor , because 128 % 1 == 0,128 % 2 == 0,128 % 8 == 0.
Self divisor Inclusion is not allowed 0 .

Given two integers left and right , Return a list , The elements of the list are ranges [left, right] All of the inside Self divisor .

Example 1：

Input ：left = 1, right = 22
Output ：[1, 2, 3, 4, 5, 6, 7, 8, 9, 11, 12, 15, 22]
Example 2:

Input ：left = 47, right = 85
Output ：[48,55,66,77]

source ： Power button （LeetCode）

How to say this question , The key is to find out every bit of a number , Let's see if it's divisible . For convenience , You can encapsulate a function to handle ：

== Ben rookie This is what we do emm, as for bosses == I don't know

922. Sort arrays by parity II

Given an array of nonnegative integers nums, nums The middle half integer is Odd number , Half the whole number is even numbers .

Sort the array , For convenience nums[i] In an odd number of ,i It's also Odd number ; When nums[i] For even when , i It's also even numbers .

You can go back to Any array that meets the above conditions is the answer .

Example 1：

Input ：nums = [4,2,5,7]
Output ：[4,5,2,7]
explain ：[4,7,2,5],[2,5,4,7],[2,7,4,5] It will also be accepted .
Example 2：

Input ：nums = [2,3]
Output ：[2,3]

source ： Power button （LeetCode）

Find half the odd numbers in the array , Find out the even number of the other half , A little manipulation of the subscript will solve the problem ：

976. The maximum circumference of a triangle

Given by some positive numbers （ Representative length ） Array of components nums , return Consisting of three lengths 、 The maximum perimeter of a triangle whose area is not zero . If we can't form any triangle with non-zero area , return 0.

Example 1：

Input ：nums = [2,1,2]
Output ：5
Example 2：

Input ：nums = [1,2,1]
Output ：0

source ： Power button （LeetCode）

Their thinking ： Put the array in order , find 3 The biggest element , Judge whether it can form a triangle ：

1287. The number of occurrences in an ordered array exceeds 25% The elements of

Give you a non decreasing Orderly An array of integers , It is known that there is exactly one integer in this array , It occurs more than the total number of elements in the array 25%.

Please find and return this integer

Example ：

Input ：arr = [1,2,2,6,6,6,6,7,10]
Output ：6

source ： Power button （LeetCode）

Literally , Just do the questions directly ：

1351. Count the negative numbers in an ordered matrix

To give you one m * n Matrix grid, The elements of a matrix, whether by row or column , All in non increasing order . Please count and return grid in negative Number of .

Example 1：

Input ：grid = [[4,3,2,-1],[3,2,1,-1],[1,1,-1,-2],[-1,-1,-2,-3]]
Output ：8
explain ： Common matrix 8 Negative numbers .
Example 2：

Input ：grid = [[3,2],[1,0]]
Output ：0

source ： Power button （LeetCode）

Traverse you

1903. The largest odd number in a string

Give you a string num , Represents a large integer . Please write in the string num All of the Non empty substring To find out in the The odd number with the largest value , And returns... As a string . If there is no odd number , Then return an empty string “” .

Substring Is a continuous sequence of characters in a string .

Example 1：

Input ：num = “52”
Output ：“5”
explain ： Non empty substrings have only “5”、“2” and “52” .“5” It's the only odd number .
Example 2：

Input ：num = “4206”
Output ：“”
explain ： stay “4206” There is no odd number in .
Example 3：

Input ：num = “35427”
Output ：“35427”
explain ：“35427” It's an odd number in itself .

source ： Power button （LeetCode）

It is more convenient to traverse from back to front , Just the last one （ Relatively speaking , The last one at present ） An odd number means that it is an odd number >, Let's start the code directly ：

1979. Find the largest common divisor of the array

Give you an array of integers nums , Returns the maximum number and the minimum number of decimals in the array greatest common divisor .

Two numbers of greatest common divisor Is the largest positive integer that can be divided by two numbers .

Example 1：

Input ：nums = [2,5,6,9,10]
Output ：2
explain ：
nums The smallest number is 2
nums The biggest number is 10
2 and 10 The greatest common divisor of 2
Example 2：

Input ：nums = [7,5,6,8,3]
Output ：1
explain ：
nums The smallest number is 3
nums The biggest number is 8
3 and 8 The greatest common divisor of 1
Example 3：

Input ：nums = [3,3]
Output ：3
explain ：
nums The smallest number is 3
nums The biggest number is 3
3 and 3 The greatest common divisor of 3

source ： Power button （LeetCode）

Their thinking ： After sorting the array , The first is the smallest element , The last dimension is the largest element , The next step is to find the greatest common divisor （ direct division algorithm Just do it ）：

2089. Find the target subscript after array sorting

I'll give you a subscript from 0 The starting array of integers nums And a target element target .

Target subscript It's a satisfaction nums[i] == target The subscript i .

take nums Press The decreasing After sequencing , Return from nums A list of target subscripts in . If there is no target subscript , Return to one empty list . The returned list must be Increasing Sequential arrangement .

Example 1：

Input ：nums = [1,2,5,2,3], target = 2
Output ：[1,2]
explain ： After ordering ,nums Turn into [1,2,2,3,5] .
Satisfy nums[i] == 2 The subscript of is 1 and 2 .
Example 2：

Input ：nums = [1,2,5,2,3], target = 3
Output ：[3]
explain ： After ordering ,nums Turn into [1,2,2,3,5] .
Satisfy nums[i] == 3 The subscript of is 3 .
Example 3：

Input ：nums = [1,2,5,2,3], target = 5
Output ：[4]
explain ： After ordering ,nums Turn into [1,2,2,3,5] .
Satisfy nums[i] == 5 The subscript of is 4 .
Example 4：

Input ：nums = [1,2,5,2,3], target = 4
Output ：[]
explain ：nums Does not contain a value of 4 The elements of .

source ： Power button （LeetCode）

take nums Press The decreasing After sequencing , This sentence shows that we need to sort first , Arrays are unordered , Later, you can traverse and search ：

Submit run ：

2124. Check all A All in B Before

To give you one only By the character ‘a’ and ‘b’ Composed string s . If in the string Every ‘a’ All appear in Every ‘b’ Before , return true ; otherwise , return false .

Example 1：

Input ：s = “aaabbb”
Output ：true
explain ：
‘a’ In the subscript 0、1 and 2 ; and ‘b’ In the subscript 3、4 and 5 .
therefore , Every ‘a’ In every ‘b’ Before , So back true .
Example 2：

Input ：s = “abab”
Output ：false
explain ：
There is one. ‘a’ In the subscript 2 , And one ‘b’ In the subscript 1 .
therefore , Can't satisfy everyone ‘a’ In every ‘b’ Before , So back false .
Example 3：

Input ：s = “bbb”
Output ：true
explain ：
non-existent ‘a’ , Therefore, it can be regarded as every ‘a’ In every ‘b’ Before , So back true .

source ： Power button （LeetCode）

Their thinking ：a Is it all there b Before , So we define two variables , One for 0 As a judgment b The subscript , For another 1 As a judgment a The subscript , Just compare directly ：

2180. Count the number of integers whose sum of figures is even

Give you a positive integer num , Please count and return Less than or equal to num And the sum of the figures is even numbers The number of positive integers of .

Positive integer The sum of your numbers Is the result of the addition of the corresponding numbers on all its bits .

Example 1：

Input ：num = 4
Output ：2
explain ：
Only 2 and 4 Satisfy less than or equal to 4 And the sum of the numbers is even .
Example 2：

Input ：num = 30
Output ：14
explain ：
Only 14 Integers must be less than or equal to 30 And the sum of the numbers is even , Namely ：
2、4、6、8、11、13、15、17、19、20、22、24、26 and 28 .

source ： Power button （LeetCode）

Find out that the sum of the figures is even numbers A positive integer of , Encapsulated into a function for easy operation ：

2278. Percentage of letters in string

Give you a string s And a character letter , Back in the s Medium is equal to letter Of characters percentage , Round down to the nearest percentage .

Example 1：

Input ：s = “foobar”, letter = “o”
Output ：33
explain ：
Equal to letter ‘o’ The characters in s The percentage of is 2 / 6 * 100% = 33% , Rounding down , So back 33 .
Example 2：

Input ：s = “jjjj”, letter = “k”
Output ：0
explain ：
Equal to letter ‘k’ The characters in s The percentage of is 0% , So back 0 .

source ： Power button （LeetCode）

There's nothing to say , We're done

summary

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