1. Small input
Empty and one-item arrays are already sorted.
if (arr.length <= 1) return arrTyporithm · hard
Radix Sort
▷ Interactive algorithm labradix-sortsortingdistributiondigitsnon-comparison
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Full lesson · 8 learning steps Open any exercise for focused practice
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Step 1 of 8 · intro card
Learn Radix Sort
Sorting Algorithms
Radix Sort sorts non-negative integers one digit place at a time using stable buckets.
Radix Sort avoids direct value comparisons and groups numbers by digits.
It starts at the ones place, then moves to tens, hundreds, and so on.
Each pass places values into buckets 0 through 9 and flattens those buckets back into the array.
The per-digit passes must be stable so earlier digit order is preserved while later digits are processed.
For bounded digit counts, the runtime is O(d * (n + b)), where d is digit count and b is bucket count.
Preparing algorithm lab…
01
Works on non-negative integer keys.
02
Process least significant digit first.
03
Use ten buckets for decimal digits.
04
Stable bucket order is essential.
05
Runtime depends on digit count, not comparisons.
function radixSort(arr) {
if (arr.length <= 1) return arr;
let max = Math.max(...arr);
let place = 1;
while (Math.floor(max / place) > 0) {
const buckets = Array.from({ length: 10 }, () => []);
for (const value of arr) {
const digit = Math.floor(value / place) % 10;
buckets[digit].push(value);
}
arr = buckets.flat();
place *= 10;
}
return arr;
}Read the implementation
Connect each part of the code to the concept before you type.
2. Largest value
The largest value tells us how many digit places to process.
let max = Math.max(...arr)3. Ones place
Start sorting by the ones digit.
let place = 14. Digit loop
Continue while the largest number still has a digit at this place.
while (Math.floor(max / place) > 0)5. Ten buckets
Decimal digits need buckets 0 through 9.
Array.from({ length: 10 }, () => [])6. Extract digit
Divide by the current place and take the last digit.
const digit = Math.floor(value / place) % 107. Place in bucket
Push preserves the order of values inside each digit bucket.
buckets[digit].push(value)8. Flatten buckets
Buckets are concatenated back into the next partially sorted array.
arr = buckets.flat()9. Next digit
Move from ones to tens, hundreds, and beyond.
place *= 10A complete learning loop
01
Understand
Read the concept map and follow the code breakdown.
02
Reconstruct
Type the implementation, repair mistakes and work through every recall exercise.
03
Verify
Use the final check without hints; revisit weak concepts in short practice sessions.