如何识别一个数组的所有元素是否存在于另一个数组中

Question

I need to create a function to check if all the letters in the second string of a two string array are present in the first string. The function I wrote seems to work for most of the examples I tried with it but ["hello" , "hey"] returns true despite there not being ay in hello and I don't understand why.

Here's my code:

function mutation(arr) {
  arr[0] =arr[0].toUpperCase().split("");
  arr[1] =arr[1].toUpperCase().split("");

  for(i=0;i<arr[1].length;i++){
    if(arr[0].indexOf(arr[1][i])>=0){
      return true;
} else {return false;}}}

mutation(["hello", "Hey"]);

Answer 1

You are returning true even if one character is matched ,Try below code it checks if all characters are present or not

    function mutation(arr) {
    arr[0] = arr[0].toUpperCase().split("");
    arr[1] = arr[1].toUpperCase().split("");
    var count = 0;

    for (i = 0; i < arr[1].length; i++) {
        if (arr[0].indexOf(arr[1][i]) >= 0) {
            count++;
        }

    }

    return count === arr[1].length

}

mutation(["hello", "Hey"]);

Answer 2

here is one more efficient solution, it works only for lowercase letters.

 (function(){ function charCode(str, i){ return str.charCodeAt(i) - 97; } function isMutation(a,b){ const aArr = new Uint8Array(26); const bArr = new Uint8Array(26); let i=0; let index = 0; while(i<a.length){ ++aArr[charCode(a, i)]; ++i; } i = 0; while(i<b.length){ ++bArr[charCode(b, i)]; ++i; } i = 0; while(i < 26){ if(!(aArr[i]===0 && bArr[i]===0 || aArr[i]>0 && bArr[i]>0)){ return false } ++i; } return true; } console.assert(isMutation('hello', 'oleh') === true); console.assert(isMutation('hello', 'hey') === false); })(); 

you can also compare sum of uniq chars in the both arrays, but in this case you have to add each letters only once.

Answer 3

I would recommend using one of the code solutions suggested by user georg at Remove Duplicates from JavaScript Array .

For example, the function below could be used to sort each array (arr[0] and arr[1]) and remove duplicates.

Credit to user georg at the link above.

function uniq(a) {
    return a.sort().filter(function(item, pos, ary) {
        return !pos || item != ary[pos - 1];
    })
}

Once you have sorted/removed duplicates, you can test to see if the two returned strings are equal or not.

Hello => EHLO, and Hey => EHY

EHLO !== EHY