# Valid anagram algorithm in JavaScript

Given two strings such as `"listen"`

and `"silent"`

, return whether or not they
are valid anagrams of each other. That is, the second word uses the same letters
as the first but potentially in a different order.

One approach is to make a frequency count of the first string, and then iterate the second string “checking off” each letter from the frequency count of the first. If we hit a missing letter or reduce the corresponding frequency count to zero, we know it’s not a valid anagram. If we’re able to check off every letter, then it is a valid anagram.

```
function validAnagram(a, b) {
if (a.length !== b.length) {
return false;
}
const freq_a = {};
for (let i = 0; i < a.length; i++) {
freq_a[a[i]] = (freq_a[a[i]] || 0) + 1;
}
for (let i = 0; i < b.length; i++) {
if (!freq_a[b[i]]) {
return false;
}
freq_a[b[i]] -= 1;
}
return true;
}
```

This algorithm is $O(n)$ as we iterate twice on the number of letters.