Find the first none-repeated character in a string, what are the mistakes here?

user_4219893 0
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I'm doing some exercises. the question is to find the first none-repeated character in a string. My idea is: turn string to array. assign array[0] to a new variable, and remove this array[0] from array. Check if this new array contain this variable, if not, return this variable. Else, use filter to remove same value elements and get a new array. repeat the process. the code as following.

const NoneReChar = (str) => {
  let tempArr = str.split('');
  let start = tempArr[0];
  while (true) {
    tempArr.shift();
    if (!tempArr.includes(start)) {
      return start;
    } else {
      tempArr.filter(char => char !== start);
      start = tempArr[0];
    }
  }
}
console.log(NoneReChar("aaaabbbeccc"))

I was expect output 'e', but I keep getting 'a'...where are the mistakes I made here?

filter arrays javascript string
2 Answers

The Array.filter() method doesn't mutate the original array. You need to assign the result of filter to tempArr:

tempArr = tempArr.filter(char => char !== start);

Example:

const NoneReChar = (str) => {
  let tempArr = str.split('');
  let start = tempArr[0];
  while (true) {
    tempArr.shift();
    if (!tempArr.includes(start)) {
      return start;
    } else {
      tempArr = tempArr.filter(char => char !== start);
      start = tempArr[0];
    }
  }
}
console.log(NoneReChar("aaaabbbeccc"))

However, you don't handle the not found case. To handle it instead of true, the while clause should stop when the array is empty:

const NoneReChar = (str) => {
  let tempArr = str.split('');
  let start = tempArr[0];
  
  while (tempArr.length) {
    tempArr.shift();
    if (!tempArr.includes(start)) {
      return start;
    } else {
      tempArr = tempArr.filter(char => char !== start);
      start = tempArr[0];
    }
  }
  
  return null;
}
console.log(NoneReChar("aabbcc"))

Another option is comparing the length of the array before and after filtering. If the length is the same, the item was not repeated:

const NoneReChar = (str) => {
  let tempArr = str.split('');
  
  while (tempArr.length) {
    const [start, ...rest] = tempArr; // take the 1st item and the rest
    
    tempArr = rest.filter(char => char !== start); // filter out start
    
    if(tempArr.length === rest.length) { // check current and previous arrays, and if the length still matches, start didn't appear again
      return start;
    }
  }
  
  return null;
}
console.log(NoneReChar("aabzbcc"))

user_51574540 
const NoneReChar = (str) => {
      const tempArr = str.split('');
      let result = 'Not Found';
      for (let index = 0; index < tempArr.length; index++) {
        const firstIndex = tempArr.indexOf(tempArr[index]);
        const lastIndex = tempArr.lastIndexOf(tempArr[index]);
        if (firstIndex === lastIndex) {
          result = tempArr[index];
          break;
        }
      }
      return result;
    }
    console.log(NoneReChar("aaaabbbeccc"));
user_96195530
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