Javascript - Count number of consecutive character occurrences-CodePudding

I have been trying to solve this problem for some time now and I have partially managed to achieve it.

I am trying to write a function that will return a nested array, each array element will contain the number of consecutive chars found in a given string.

For example: for the given string "aaaabccaadeeee", the function should return nested array [[4, a] [1, b] [2, c] [2, a] [1, d][4, e]]

I have managed to write the following function but it returns [ [ 4, 'b' ], [ 0, 'c' ], [ 1, 'a' ], [ 1, 'd' ], [ 0, 'e' ] ]

What am I doing wrong?

function consecutiveArray(str) {

  const chunks = str.split("");
  let counter = 0;
  const finalArray = [];
  let  prevItem;


  for(chunk of chunks){

    if(!prevItem || prevItem === chunk){
      counter  
    } else {
      finalArray.push([counter, chunk])
      counter=0;
    }

    
    prevItem = chunk;
  }

  

  return finalArray;
  
}


console.log(consecutiveArray('aaaabccaadeeee'))

CodePudding user response：

You can use String.matchAll to match all the groups of characters in your string; then just iterate the matches to produce your desired result:

const str = 'aaaabccaadeeee'

const res = Array.from(str.matchAll(/(.)\1*/g)).map(([m, g]) => [m.length, g])

console.log(res)

CodePudding user response：

Your else clause is wrong, you should push the counter for prevItem and initialize the count to 1. Also, push the final counter the after the loop.

function consecutiveArray(str) {
  const chunks = str.split("");
  let counter = 0;
  const finalArray = [];
  let  prevItem;
  for(chunk of chunks){
    if(!prevItem || prevItem === chunk){
      counter  
    } else {
      finalArray.push([counter, prevItem])
      counter=1;
    }
    prevItem = chunk;
  }
  finalArray.push([counter, prevItem])
  return finalArray;
}
console.log(consecutiveArray('aaaabccaadeeee'))

CodePudding user response：

Here is another way of doing it without RegExp:

const str="aaaabccaadeeee";

const res=[];
str.split("").reduce((a,c,i)=>{
 if(a!==c) res.push([0,c]);
   res.at(-1)[0];
 return c;
},null);
console.log(res);
// for comparison: Nick's solution:
console.log([...str.matchAll(/(.)\1*/g)].map(([m,g])=>[m.length,g]))