Find unique characters in a string and the count of their occurrences

July 12, 2022

I need to count the occurrence of characters in a given string and print out the unique characters and the number of how many times they appeared. So, for example, if I receive a string of ‘HELLO’ it should print out:

H: 1,
E: 1,
L: 2,
O: 1

This is a much-simplified version of a problem, but the answer should put me in the right direction. How can I approach this problem?

Thank you in advance.

>Solution :

My approach to this problem is:

let str = "HELLO";

// An object for the final result {character:count}
let counts = {};

// Loop through the str...
for (let index = 0; index < str.length; ++index) {
  // Get each char
  let ch = str.charAt(index);
  // Get the count for that char
  let count = counts[ch];
  // If we have one, store that count plus one;
  if (count) {
    counts[ch] += 1;
  } else {
    // if not, store one
    counts[ch] = 1;
  }
  // or more simply with ternary operator
  //   counts[ch] = count ? count + 1 : 1;.
}
console.log(counts);