我的老板现在要我实现一种机制，使他可以搜索数组中的项目，并为他提供该值所在的索引。

你的任务：

编写一个程序或函数，该程序或函数接收一个数组和一个值（字符串，整数，浮点数或布尔值），并返回出现该值的数组的索引（0或1索引，以您喜欢的为准）。如果该值不在数组中，则返回一个空数组。

输入：

A中可能存在或不存在的数组A和值V。

输出：

包含V在A中出现的索引的数组，如果V在A中不出现，则为空数组。

测试用例：

请注意，测试用例基于0。

12, [12,14,14,2,"Hello World!",3,12,12]         -> [0,6,7]
"Hello World", ["Hi", "Hi World!", 12,2,3,True] -> []
"a", ["A",True,False,"aa","a"]                  -> [4]
12, [12,"12",12]                                -> [0,2]

得分：

这是代码高尔夫球，因此以字节为单位的最低分数获胜。

Pyth，2个字节

0索引。

xE

在线尝试！或检查所有测试用例

说明

xEQ  - Full Program. Takes Input from standard input. Q means evaluated input and is implicit at the end of the program.

x   - Get all the indexes of x in y
 E  - Evaluated Input #2 - The value
  Q - The list - Evaluated Input #1

MATL，2个字节

mf

的 m消耗两个参数，并且检查该阵列中的每个元素是否等于另一个参数，f返回一个阵列的truthy条目的索引。

在线尝试！

Python 3 3，45字节

-3个字节，感谢@EriktheOutgolfer和@Chris_Rands

lambda y,x:[i for i,j in enumerate(x)if j==y]

测试套件。

今天我学到了 enumerate(x) == zip(range(len(x)),x)。

Python 3，47个字节

lambda n,l:[x for x in range(len(l))if l[x]==n]

在线尝试！或检查所有测试用例

R（+ pryr），20个字节

pryr::f(which(a==b))

对功能求值

function (a, b) 
which(a == b)

无论在哪里a能值来寻找和b载体，或者周围的其他方法。当出现两个长度不等的向量（R中的一个值算作长度为1的向量）时，R将包裹较短的一个以匹配较长的一个的长度。然后检查相等性。这产生逻辑向量。which提供此向量为true的索引。

在线尝试！

JavaScript，39个字节

e=>a=>[...a.keys()].filter(i=>a[i]===e)

f=
e=>a=>[...a.keys()].filter(i=>a[i]===e)

console.log(f(12)([12,14,14,2,"Hello World!",3,12,12]));
console.log(f("Hello World")(["Hi", "Hi World!", 12,2,3,true]));
console.log(f("a")(["A",true,false,"aa","a"])); 
console.log(f(12)([12,14,14,2,"Hello World!",3,12,'12']));

上面的代码片段可能不适用于所有浏览器，因此这里是一个TIO链接。

JavaScript（ES6），44 43字节

^{划掉44仍然是常规44;（}

v=>a=>a.map((x,i)=>x===v&&++i).filter(x=>x)

@Arnauld 节省了1个字节

let f=
v=>a=>a.map((x,i)=>x===v&&++i).filter(x=>x)
;

console.log(f(12)([12,14,14,2,"Hello World!",3,12,12]));         // => [1,7,8]
console.log(f("Hello World")(["Hi", "Hi World!", 12,2,3,true])); // => []
console.log(f("a")(["A",true,false,"aa","a"]));                  // => [5]

05AB1E，4个字节

QāsÏ

在线尝试！

1个索引。

C＃，88 72字节

using System.Linq;a=>o=>a.Select((i,n)=>o.Equals(i)?n:-1).Where(n=>n>=0)

@LiefdeWen节省了16个字节。

在线尝试！

果冻，3个字节

⁼€T

在线尝试！

-1 thanks to Mr. Xcoder. (dyadic chains)

Haskell, 41 39 bytes

v!l=fst<$>(filter((==v).snd)$zip[1..]l)

Try it online!

Saved two bytes thanks to @flawr

Haskell is statically typed, so I had to use a little workaround to run the test cases.

Husk, 5 bytes

`fNm=

Try it online! 1-indexed.

Explanation

       -- implicitly input a value v and a list L
   m=  -- map "equals v" over the list L, resulting in a list of truthy and falsy values
`fN    -- filter the natural numbers N by discarding the numbers at falsy positions 
          and keeping the ones at truthy positions

Ruby, 46 40 39 bytes

->e,a{i=-1;a.map{|x|i+=1;x==e&&i}-[!1]}

Saved 7 bytes!!! thanks to Eric Duminil.

Try it online.

Ruby, 38 bytes

->e,a{a.each_index.select{|x|a[x]==e}}

Try it online!

Google Sheets, 101 bytes

=IfError(Join(",",Filter(Column(Offset(A1,0,0,1,Counta(Split(B1,",")))),Exact(Split(B1,","),A1))),"")

Value V in A1 and array A in B1 with each entry separated by a comma. Null entires are not allowed (row 5 below shows what happens).

Explanation:

Offset(A1,0,0,1,Counta(Split(B1,","))) returns a range that is one row tall and as many columns wide as there are entries in A1.

=IfError(Join(",",Filter(Column(~),Exact(Split(B1,","),A1))),"") filters the column numbers of that range based on whether or not the value in A1 is exactly each of the values in B1 and concatenates them all in a comma-delineated list.

Clojure, 40 bytes

First attempt at code golf.

keep-indexed maps a function over a collection here, passing the current index into the callback and yielding any non-nil return values.

(fn[a b](keep-indexed #(if(= %2 a)%1)b))

Try it online!

APL (Dyalog Unicode), 2 bytes^SBCS

Takes item to look for as left argument (must be scalar to find an item of the lookup array rather than a subarray) and the lookup array (which may have up to 15 dimensions) as right argument. Returns list of indices, each of which may has as many elements as the number of dimensions in the lookup array.

⍸⍷

Try it online!

⍸ ɩndices where

⍷ found

Batch, 86 bytes

@set i=0
:g
@if "%~2"=="" exit/b
@if %1==%2 echo %i%
@set/ai+=1
@shift/2
@goto g

Takes input as command line parameters (value then the array elements as separate parameters). Note: String quoting is considered part of the match e.g. "1" won't equal 1 (would cost 6 bytes).

Python 2, 49 bytes

lambda l,v:filter(lambda i:l[i]==v,range(len(l)))

Try it online!

Not short enough, but I thought it was cool. ¯\_(ツ)_/¯

Perl 5, 28 bytes

sub{grep$_[$_]eq$_[0],1..@_}

Try it online!

The output is 1-indexed.
An anonymous function is quite unusual for Perl, but it happens to be the shortest I could think of. grep ..., 1 .. @_ iterates over the indexes of the input array (actually it goes one cell beyond the last, but it doesn't matter), keeping only the index that satisfy $_[$_]eq$_[0], ie. the ones where the value of the element ($_[$_]) is the same as the value we need to keep ($_[0]).

Slightly longer (31 bytes (30 + -l flag)), but as a full program:

$@=<>;$@eq$_&&print$.-1while<>

Try it online!

Haskell, 37 33 bytes

import Data.List
findIndices.(==)

Thanks @Laikoni for -4 bytes!

Try it online!

Java 8, 146 113 112 111 110 108 bytes

import java.util.*;l->o->{List r=new Stack();for(int i;(i=l.indexOf(o))>-1;l.set(i,null))r.add(i);return r;}

-2 bytes thanks to @TAsk by using Vector instead of ArrayList.
-1 byte by using Stack instead of Vector.
-2 bytes thanks to @Jakob by inputting a ArrayList instead of an array.

0-indexed

Explanation:

Try it here.

import java.util.*;    // Required import for Vector and Vector
l->o->{                // Method with List and Object parameters
  List r=new Stack();  //  Result-list
  for(int i;(i=l.indexOf(o))>=-1;
                       //  Loop as long as we can find the object in the list
    l.set(i,null))     //   After every iteration, remove the found item from the list
      r.add(i);        //    Add the index to the result-list
                       //  End of loop (implicit / single-line body)
  return r;            //  Return the result-List
}                      // End of method

05AB1E, 4 bytes

Qƶ0K

Try it online!

It is 1-indexed, as shown below:

IN A-#------------------------> [2,3,3,3,4]
IN B-#------------------------> 3
-----#------------------------+-----------------
Q    # Vectorized equivalence | [0,1,1,1,0]
 ƶ   # Lift by index          | [0,2,3,4,0]
  0K # Remove zeros           | [2,3,4]

Mathematica, 12 bytes

Position@##&

1-Indexed

input [Array,Value]

[{12, 14, 14, 2, "Hello World!", 3, 12, 12}, 12]

output

{{1}, {7}, {8}}

Haskell, 29 bytes

e#l=[i|(i,h)<-zip[0..]l,h==e]    

Try it online!

Japt, 9 bytes

mȶV©YÄÃf

1-indexed.

Japt input doesn't support booleans, so they have been replaced with 0 and 1 in the test cases.

Try it online! with the -Q flag to format the array output.

0-indexed Solution, 11 bytes

l o f@gX ¶V

Try it online!

Perl 6, 21 bytes

{grep :k,*===$^v,@^z}

Try it online!

The :k adverb to grep tells it to return the matching keys (indices) of the input sequence that match the predicate * === $^v.

If strings and numbers were considered equivalent, one could use a grep predicate of just $^v instead of * === $^v.

Common Lisp, 66 bytes

(lambda(x s)(loop as i in s as j from 0 when(equal i x)collect j))

Try it online!

TXR Lisp, 26 bytes

(op where(op equal @@1)@2)

In other words, "Where is argument 2 equal to argument 1?"

Run:

1> (op where(op equal @@1) @2)
#<interpreted fun: lambda (#:arg-01-0166 #:arg-02-0167 . #:rest-0165)>
2> [*1 12 #(12 14 14 2 "Hello world!" 3 12 12)]
(0 6 7)
3> [*1 "Hello World" #("Hi" "Hi world!" 12 2 3 t)]
nil

Clojure, 39 38 bytes

#(filter(comp #{%2}%)(range(count %)))

A bit obscure :) The first input argument is a vec of values and the second one is the searched value. % maps indexes to values, and the set #{%2} returns truthy (the input argument %2) or falsy nil for that value. comp composes these together.

C 340 362 166 115 Bytes

Hello all. My first time here. I figured since I enjoy (attempting) to write optimized code I may as well give this a try.

@Rodney - ~39 bytes from the includes

@Zacharý - 7 bytes with implicit typing

0-indexed.

How to Run:

As per @Arnolds suggestion, the program takes arguments in a much more C friendly manner. This let me reduce the size of the file by a little more than half.

The arguments should be passed in the following order value [element1 ...] where braces indicate optional arguments

You may or may not have to add escaped quotes to any strings that are provided in order to satisfy the condition of 12 != "12". On my system the this can be done in the following manner

prog-name.exe 12 3 "Hello" 12 4 "12"
Returns [2,4]     < This is incorrect

prog-name.exe 12 3 "\"Hello\"" 12 4 "\"12\""
Returns [2]       < Correct

golfed

#define P printf(
b=0;main(int c,char**v){P"[");for(--c;c-1;c--)b|=strcmp(v[1],v[c])?0:P b?",%i":"%i",c-2);P"]");}

ungolfed

#define P printf(

//Implicit only works in global(I totally knew this after almost 4 years of C :P)
b = 0;
main(int c,char**v)
{

    P"[");

    //match loop
    //b is used to determine if this is the first iteration. it can be assumed that printf will always return >0
    //subract two from c to get correct index number of match
    for(--c; c-1; c--)
        b |= strcmp(v[1], v[c]) ? 0 : P b ? ",%i" : "%i", c-2);

    P"]");

    return 0;
}