Find All Anagrams in a String

mediumcodingAlgorithmsSliding WindowHash MapStrings~30 min

Asked at Google, Meta

Overview

Given two strings s and p, return an array of all start indices of p's anagrams in s. An anagram uses all letters exactly.

Constraints

1 <= s.length, p.length <= 30,000
Both consist of lowercase English letters.

Examples

findAnagrams("cbaebabacd", "abc");
// => [0, 6]  ("cba" at 0, "bac" at 6)

findAnagrams("abab", "ab");
// => [0, 1, 2]

Solution

Reveal solution

function findAnagrams(s, p) {
  const result = [];
  const pCount = new Array(26).fill(0);
  const sCount = new Array(26).fill(0);
  const a = 'a'.charCodeAt(0);
  for (const c of p) pCount[c.charCodeAt(0) - a]++;
  for (let i = 0; i < s.length; i++) {
    sCount[s.charCodeAt(i) - a]++;
    if (i >= p.length) sCount[s.charCodeAt(i - p.length) - a]--;
    if (sCount.every((v, j) => v === pCount[j])) result.push(i - p.length + 1);
  }
  return result;
}

Resources

Find All Anagrams in a String — LeetCode

find-all-anagrams-in-string.js

Find All Anagrams in a String

mediumcodingAlgorithmsSliding Window

Overview

Given two strings s and p, return an array of all start indices of p's anagrams in s. An anagram uses all letters exactly.

Constraints

1 <= s.length, p.length <= 30,000
Both consist of lowercase English letters.

Examples

findAnagrams("cbaebabacd", "abc");
// => [0, 6]  ("cba" at 0, "bac" at 6)

findAnagrams("abab", "ab");
// => [0, 1, 2]

Solution

Reveal solution

function findAnagrams(s, p) {
  const result = [];
  const pCount = new Array(26).fill(0);
  const sCount = new Array(26).fill(0);
  const a = 'a'.charCodeAt(0);
  for (const c of p) pCount[c.charCodeAt(0) - a]++;
  for (let i = 0; i < s.length; i++) {
    sCount[s.charCodeAt(i) - a]++;
    if (i >= p.length) sCount[s.charCodeAt(i - p.length) - a]--;
    if (sCount.every((v, j) => v === pCount[j])) result.push(i - p.length + 1);
  }
  return result;
}

Resources

Find All Anagrams in a String — LeetCode

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