How to Fix Find All Anagrams in String Errors

In this tutorial, you'll learn about How to Fix Find All Anagrams in String Errors. We cover key concepts, practical examples, and best practices.

Fix find all anagrams in string errors when character count comparison not reset or window not properly tracked.

Quick Fix

Wrong

def ana(s,p):
    ns,np=len(s),len(p)
    if ns<np: return []
    sc=Counter(s[:np]); pc=Counter(p)
    res=[0] if sc==pc else []
    for i in range(np,ns):
        sc[s[i]]+=1
        sc[s[i-np]]-=1
        if sc[s[i-np]]==0: del sc[s[i-np]]
        if sc==pc: res.append(i-np+1)
    return res

Deleting zero-count keys is optional but good practice. Works without it.

Right

from collections import Counter
def ana(s,p):
    ns,np=len(s),len(p)
    if ns<np: return []
    sc=Counter(s[:np]); pc=Counter(p)
    res=[0] if sc==pc else []
    for i in range(np,ns):
        sc[s[i]]+=1; sc[s[i-np]]-=1
        if sc[s[i-np]]==0: del sc[s[i-np]]
        if sc==pc: res.append(i-np+1)
    return res

s='cbaebabacd', p='abc' -> [0,6] (substrings 'cba','bac'). O(n).

Prevention

Sliding window counter. Add new char, remove old char, compare counters.

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FAQ