25
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Introduction

Consider a sequence of integers and one of its subsequences, say A = [4 2 2 4 4 6 5] and B = [2 4 5]. We want to remove the elements of B from A in order, and there are several ways of doing that:

A = 4 2 2 4 4 6 5
B =   2   4     5
 -> 4   2   4 6

A = 4 2 2 4 4 6 5
B =     2 4     5
 -> 4 2     4 6

A = 4 2 2 4 4 6 5
B =   2     4   5
 -> 4   2 4   6

A = 4 2 2 4 4 6 5
B =     2   4   5
 -> 4 2   4   6

In all cases, the remaining sequence is the same, [4 2 4 6]. If this happens, we say that B is uniquely removable from A.

The task

Your inputs are two sequences of nonnegative integers, A and B, where B is guaranteed to be a subsequence of A. The inputs may be equal, and they may be empty. You can take them in any order you want, in any reasonable format.

Your output shall be a truthy value if B is uniquely removable from A, and a falsy value if not.

Rules and scoring

You can write a full program or a function. The lowest byte count wins.

Test cases

[] [] -> True
[0,3] [] -> True
[1,0,1] [1] -> False
[0,2] [0,2] -> True
[2,2,1,1,2,2,2] [2,1] -> True
[4,2,2,4,4,6,5] [4,5] -> False
[10,5,10,10,5,10] [10,5,10] -> False
[4,2,2,4,4,6,5] [2,4,5] -> True
[1,1,1,0,0,0,1,1,1,0] [1,0,1,1] -> True
[0,1,0,0,0,0,1,1,0,1] [1,0,1,1] -> False
[0,4,0,0,4,1,4,2,2] [0,0,0,1,4] -> True
[0,2,2,25,0,2,2,26,0,0,2] [2,0,0,0,2] -> True
[1,1,1,3,2,1,3,2,2,3,3,2] [1,1,2,3,2] -> False
[0,3,2,0,1,3,2,0,0,0,3,2] [0,1,2,0,3] -> False
[5,7,2,7,7,1,7,7,5,2,7,7,5,2,2,7,5] [2,7,5,7,7,2] -> False
[5,4,0,5,4,5,4,1,0,4,2,1,1,2,4,4,0,2,2,1] [4,0,1,1,2,1] -> False
[0,1,4,0,1,4,0,1,5,1,4,4,2,0,0,1,1,1,2,4] [0,1,0,0,2,0,1,4] -> True
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6
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Haskell, 90 84 bytes

a%[]=[a]
(t:z)%x@(s:y)=[a|a<-z%y,t==s]++[t:s|s<-z%x]
_%_=[]
((all=<<(==).head).).(%)

Construct the list of all possible subtracted sequences nondeterministically and checks whether they are all equal.

Usage:

*Main> mapM_(\(a,b)->let r=(((all=<<(==).head).).(%)) a b in putStrLn$concat[show a," ",show b," -> ",show r]) [([],[]), ([0,3],[]), ([1,0,1],[1]), ([0,2],[0,2]), ([2,2,1,1,2,2,2],[2,1]), ([4,2,2,4,4,6,5],[4,5]), ([10,5,10,10,5,10],[10,5,10]), ([4,2,2,4,4,6,5],[2,4,5]), ([1,1,1,0,0,0,1,1,1,0],[1,0,1,1]), ([0,1,0,0,0,0,1,1,0,1],[1,0,1,1]), ([0,4,0,0,4,1,4,2,2],[0,0,0,1,4]), ([0,2,2,25,0,2,2,26,0,0,2],[2,0,0,0,2]), ([1,1,1,3,2,1,3,2,2,3,3,2],[1,1,2,3,2]), ([0,3,2,0,1,3,2,0,0,0,3,2],[0,1,2,0,3]), ([5,7,2,7,7,1,7,7,5,2,7,7,5,2,2,7,5],[2,7,5,7,7,2]), ([5,4,0,5,4,5,4,1,0,4,2,1,1,2,4,4,0,2,2,1],[4,0,1,1,2,1]), ([0,1,4,0,1,4,0,1,5,1,4,4,2,0,0,1,1,1,2,4],[0,1,0,0,2,0,1,4])]
[] [] -> True
[0,3] [] -> True
[1,0,1] [1] -> False
[0,2] [0,2] -> True
[2,2,1,1,2,2,2] [2,1] -> True
[4,2,2,4,4,6,5] [4,5] -> False
[10,5,10,10,5,10] [10,5,10] -> False
[4,2,2,4,4,6,5] [2,4,5] -> True
[1,1,1,0,0,0,1,1,1,0] [1,0,1,1] -> True
[0,1,0,0,0,0,1,1,0,1] [1,0,1,1] -> False
[0,4,0,0,4,1,4,2,2] [0,0,0,1,4] -> True
[0,2,2,25,0,2,2,26,0,0,2] [2,0,0,0,2] -> True
[1,1,1,3,2,1,3,2,2,3,3,2] [1,1,2,3,2] -> False
[0,3,2,0,1,3,2,0,0,0,3,2] [0,1,2,0,3] -> False
[5,7,2,7,7,1,7,7,5,2,7,7,5,2,2,7,5] [2,7,5,7,7,2] -> False
[5,4,0,5,4,5,4,1,0,4,2,1,1,2,4,4,0,2,2,1] [4,0,1,1,2,1] -> False
[0,1,4,0,1,4,0,1,5,1,4,4,2,0,0,1,1,1,2,4] [0,1,0,0,2,0,1,4] -> True

Thanks to @Zgarb for saving 6 bytes!

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  • \$\begingroup\$ You can rearrange things and have x%_=x for the second case of %. Also, I think the main function would be shorter in pointful form. \$\endgroup\$ – Zgarb Dec 5 '16 at 11:50
  • \$\begingroup\$ @Zgarb x%_=x won't work because the types won't match but _%_=[] saves a byte. \$\endgroup\$ – Angs Dec 5 '16 at 11:56
4
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JavaScript (ES6), 141 152 156 159

Recursive function - quite long

f=(a,b,i=0,j=0,r=a,S=new Set)=>(1/b[j]?1/a[i]&&f(a,b,i+1,j,r,S,a[i]-b[j]||f(a,b,i+1,j+1,r=[...r],r[i]=S)):S.add(0+r.filter(x=>1/x)),S.size<2)

Less golfed

f=(a, b, 
   i = 0, // current position to match in a
   j = 0, // current position to match in b
   r = a, // current result so far, A with elements of B removed - start == A
   S = new Set // set of possible "A removed B"
) => (
    1 / b[j] // check if j is still inside B
    ? 1 / a[i] // if i is inside A
      && (
        // in any case try to find current element of B in the remaining part of A
        f(a, b, i+1, j, r, S),
        a[i] == b[j] // if match was found between A and B
        && 
          // mark current element in a copy of r and 
          // look for the next element of B in the remaining part of A
          f(a, b, i+1, j+1, r=[...r], r[i]=S),
      )
    // else - j is not inside B, we have a solution in r
    // use filter to get a copy without the marked elements
    //  (note: 1/any_number == number_not_0, 1/Object == NaN)
    // then convert to string, to use as a key in S
    : S.add(0+a.filter(x=>1/x)),
    S.size<2 // return true if S has only 1 element
)  

Test

f=(a,b,i=0,j=0,r=a,S=new Set)=>(1/b[j]?1/a[i]&&f(a,b,i+1,j,r,S,a[i]-b[j]||f(a,b,i+1,j+1,r=[...r],r[i]=S)):S.add(0+r.filter(x=>1/x)),S.size<2)


out=(...x)=>O.textContent+=x.join` `+'\n'
;`[] [] -> True
[0,3] [] -> True
[1,0,1] [1] -> False
[0,2] [0,2] -> True
[2,2,1,1,2,2,2] [2,1] -> True
[4,2,2,4,4,6,5] [4,5] -> False
[10,5,10,10,5,10] [10,5,10] -> False
[4,2,2,4,4,6,5] [2,4,5] -> True
[1,1,1,0,0,0,1,1,1,0] [1,0,1,1] -> True
[0,1,0,0,0,0,1,1,0,1] [1,0,1,1] -> False
[0,4,0,0,4,1,4,2,2] [0,0,0,1,4] -> True
[0,2,2,25,0,2,2,26,0,0,2] [2,0,0,0,2] -> True
[1,1,1,3,2,1,3,2,2,3,3,2] [1,1,2,3,2] -> False
[0,3,2,0,1,3,2,0,0,0,3,2] [0,1,2,0,3] -> False
[5,7,2,7,7,1,7,7,5,2,7,7,5,2,2,7,5] [2,7,5,7,7,2] -> False
[5,4,0,5,4,5,4,1,0,4,2,1,1,2,4,4,0,2,2,1] [4,0,1,1,2,1] -> False
[0,1,4,0,1,4,0,1,5,1,4,4,2,0,0,1,1,1,2,4] [0,1,0,0,2,0,1,4] -> True`
.split('\n').forEach(t=>{
  var [a,b,_,k]=t.match(/\S+/g)
  var r=f(eval(a),eval(b))
  out(r==(k[0]=='T')?'OK':'KO',a,b,r,k)
})
<pre id=O></pre>

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3
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Pyth - 27 bytes

On mobile in school right now, so not fully golfed.

JE!t{.DLQfqJ@LQT{I#{SM^UQlJ

Test Suite

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3
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JavaScript (ES6), 116 114 113 bytes

Returns false or true.

(a,b,p)=>((F=(a,i,m)=>1/b[i]?a.map((n,j)=>m>j|n-b[i]||F(a.filter((_,k)=>j-k),i+1,j)):p?r|=p!=a:p=a+'')(a,r=0),!r)

Formatted and commented

(                                     // given:
  a, b,                               // - a, b = input arrays
  p                                   // - p = reference pattern, initially undefined
) => (                                //
  (F = (                              // F is our recursive search function, with:
    a,                                // - a = current working copy of the main array
    i,                                // - i = index in 'b'
    m                                 // - m = minimum index of matching values in 'a'
  ) =>                                //
    1 / b[i] ?                        // if we haven't reached the end of 'b':
      a.map((n, j) =>                 //   for each element 'n' at index 'j' in 'a':
        m > j | n - b[i] ||           //     if 'n' is a valid matching value,
        F(                            //     do a recursive call to F(), using:
          a.filter((_, k) => j - k),  //     - a copy of 'a' without the current element
          i + 1,                      //     - the next index in 'b'
          j                           //     - 'j' as the new minimum index in 'a'
        )                             //
      )                               //
    :                                 // else:
      p ?                             //   if the reference pattern is already set:
        r |= p != a                   //     check if it's matching the current 'a'
      :                               //   else:
        p = a + ''                    //     set the current 'a' as the reference pattern
  )(a, r = 0),                        //  initial call to F() + initialization of 'r'
  !r                                  //  yields the final result
)                                     //

Test cases

let f =

(a,b,p)=>((F=(a,i,m)=>1/b[i]?a.map((n,j)=>m>j|n-b[i]||F(a.filter((_,k)=>j-k),i+1,j)):p?r|=p!=a:p=a+'')(a,r=0),!r)

console.log(f([],[]));                                                        // -> true
console.log(f([0,3],[]));                                                     // -> true
console.log(f([1,0,1],[1]));                                                  // -> false
console.log(f([0,2],[0,2]));                                                  // -> true
console.log(f([2,2,1,1,2,2,2],[2,1]));                                        // -> true
console.log(f([4,2,2,4,4,6,5],[4,5]));                                        // -> false
console.log(f([10,5,10,10,5,10],[10,5,10]));                                  // -> false
console.log(f([4,2,2,4,4,6,5],[2,4,5]));                                      // -> true
console.log(f([1,1,1,0,0,0,1,1,1,0],[1,0,1,1]));                              // -> true
console.log(f([0,1,0,0,0,0,1,1,0,1],[1,0,1,1]));                              // -> false
console.log(f([0,4,0,0,4,1,4,2,2],[0,0,0,1,4]));                              // -> true
console.log(f([0,2,2,25,0,2,2,26,0,0,2],[2,0,0,0,2]));                        // -> true
console.log(f([1,1,1,3,2,1,3,2,2,3,3,2],[1,1,2,3,2]));                        // -> false
console.log(f([0,3,2,0,1,3,2,0,0,0,3,2],[0,1,2,0,3]));                        // -> false
console.log(f([5,7,2,7,7,1,7,7,5,2,7,7,5,2,2,7,5],[2,7,5,7,7,2]));            // -> false
console.log(f([5,4,0,5,4,5,4,1,0,4,2,1,1,2,4,4,0,2,2,1],[4,0,1,1,2,1]));      // -> false
console.log(f([0,1,4,0,1,4,0,1,5,1,4,4,2,0,0,1,1,1,2,4],[0,1,0,0,2,0,1,4]));  // -> true

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  • \$\begingroup\$ Wow! I tried to find a way to recurse with a reduced copy of A, but no success \$\endgroup\$ – edc65 Dec 7 '16 at 15:38
1
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MATL, 27 bytes

n:inXN!"1G@&)w2G=?}x]]tvdz~

The longest test cases run out of time in the online compiler.

Try it online!

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1
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JavaScript (Firefox 30+), 159 147 bytes

f=(a,b,i=f(a,b,0))=>i?i.every(x=>x+""==i[0]):b+b?a+a&&[for(n of a)if(a[i++]==b[0])for(x of f(a.slice(i),b.slice(1),0))[...a.slice(0,i-1),...x]]:[a]

Here's a couple of alternate approaches, both anonymous functions:

(a,b,f=(a,b,i=0)=>b+b?a+a&&[for(n of a)if(a[i++]==b[0])for(x of f(a.slice(i),b.slice(1)))[...a.slice(0,i-1),...x]]:[a],c=f(a,b))=>c.every(x=>x+""==c[0])
(a,b,f=(a,b,i=0)=>b+b?a+a&&[for(n of a)if(a[i++]==b[0])for(x of f(a.slice(i),b.slice(1)))[...a.slice(0,i-1),...x]]:[a])=>new Set(f(a,b).map(btoa)).size<2

Test snippet

f=(a,b,i=f(a,b,0))=>i?i.every(x=>x+""==i[0]):b+b?a+a&&[for(n of a)if(a[i++]==b[0])for(x of f(a.slice(i),b.slice(1),0))[...a.slice(0,i-1),...x]]:[a]

T.textContent = T.textContent.split`
`.map(x => x + ` (${f(...x.split` `.slice(0,2).map(eval))})`).join`
`
<pre id=T>[] [] -> True
[0,3] [] -> True
[1,0,1] [1] -> False
[0,2] [0,2] -> True
[2,2,1,1,2,2,2] [2,1] -> True
[4,2,2,4,4,6,5] [4,5] -> False
[10,5,10,10,5,10] [10,5,10] -> False
[4,2,2,4,4,6,5] [2,4,5] -> True
[1,1,1,0,0,0,1,1,1,0] [1,0,1,1] -> True
[0,1,0,0,0,0,1,1,0,1] [1,0,1,1] -> False
[0,4,0,0,4,1,4,2,2] [0,0,0,1,4] -> True
[0,2,2,25,0,2,2,26,0,0,2] [2,0,0,0,2] -> True
[1,1,1,3,2,1,3,2,2,3,3,2] [1,1,2,3,2] -> False
[0,3,2,0,1,3,2,0,0,0,3,2] [0,1,2,0,3] -> False
[5,7,2,7,7,1,7,7,5,2,7,7,5,2,2,7,5] [2,7,5,7,7,2] -> False
[5,4,0,5,4,5,4,1,0,4,2,1,1,2,4,4,0,2,2,1] [4,0,1,1,2,1] -> False
[0,1,4,0,1,4,0,1,5,1,4,4,2,0,0,1,1,1,2,4] [0,1,0,0,2,0,1,4] -> True</pre>

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  • \$\begingroup\$ I like the snippet too \$\endgroup\$ – edc65 Dec 5 '16 at 19:06
1
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Mathematica, 128 bytes

h=Length;n=ToExpression;g=ToString;y=Array;h@Union@ReplaceList[#2,n@Riffle[y["a"<>g@#<>"___"&,t=h@#+1],#]->n@y["a"<>g@#&,t]]==1&

Unnamed function taking two list arguments, where the first is the subsequence and the second is the full sequence; outputs True or False.

The core part is the following sequence, ungolfed for readability:

ReplaceList[#2, ToExpression @
  Riffle[
    Array["a" <> ToString@# <> "___" &, Length@# + 1]
    , #
  ] -> ToExpression @ 
    Array["a" <> ToString@#& , Length@# + 1 ]
]

Here # represents the subsequence—for example, {2,4,5}. The first Array command creates a list of strings like {"a1___","a2___","a3___","a4___"}, which is then Riffled together with # to yield a weird list like {"a1___",2,"a2___",4,"a3___",5,"a4___"}; then this list is cast into an actual Mathematica expression. For the example {2,4,5}, a partial evaluation of this core code is

ReplaceList[#2, {a1___,2,a2___,4,a3___,5,a4___} -> {a1,a2,a3,a4}]

which exactly gives a list of all possible ways to remove the subsequence {2,4,5} from #2 and leave the rest of the list alone.

After this list is generated, we simply remove duplicates using Union and test whether the length of the resulting output is 1 or not.

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