Dsa Sort Radix

In this tutorial, you'll learn about How to Fix Radix Sort Errors. We cover key concepts, practical examples, and best practices.

Fix radix sort errors when digit extraction doesn't use stable sub-sort or base choice is wrong.

Quick Fix

Wrong

def rs(a):
    m=max(a); exp=1
    while m//exp>0:
        n=len(a); out=[0]*n; cnt=[0]*10
        for x in a: cnt[(x//exp)%10]+=1
        out[cnt[(x//exp)%10]-1]=x
        # Wrong: doesn't use prefix sum for stable placement

No prefix sum. Doesn't produce stable sort within digit.

Right

def rs(a):
    m=max(a); exp=1
    while m//exp>0:
        n=len(a); out=[0]*n; cnt=[0]*10
        for x in a: cnt[(x//exp)%10]+=1
        for i in range(1,10): cnt[i]+=cnt[i-1]
        for x in reversed(a):
            d=(x//exp)%10; cnt[d]-=1; out[cnt[d]]=x
        a=out; exp*=10
    return a

[170,45,75,90,802,24,2,66] -> [2,24,45,66,75,90,170,802]. O(d*(n+k)).

Prevention

Use counting sort as stable sub-routine per digit. Process from least significant digit.

DodaTech Tools

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