# 2781. Length of the Longest Valid Substring

## Description

You are given a string word and an array of strings forbidden.

A string is called valid if none of its substrings are present in forbidden.

Return the length of the longest valid substring of the string word.

A substring is a contiguous sequence of characters in a string, possibly empty.

Example 1:

Input: word = "cbaaaabc", forbidden = ["aaa","cb"]
Output: 4
Explanation: There are 11 valid substrings in word: "c", "b", "a", "ba", "aa", "bc", "baa", "aab", "ab", "abc" and "aabc". The length of the longest valid substring is 4.
It can be shown that all other substrings contain either "aaa" or "cb" as a substring. 

Example 2:

Input: word = "leetcode", forbidden = ["de","le","e"]
Output: 4
Explanation: There are 11 valid substrings in word: "l", "t", "c", "o", "d", "tc", "co", "od", "tco", "cod", and "tcod". The length of the longest valid substring is 4.
It can be shown that all other substrings contain either "de", "le", or "e" as a substring.


Constraints:

• 1 <= word.length <= 105
• word consists only of lowercase English letters.
• 1 <= forbidden.length <= 105
• 1 <= forbidden[i].length <= 10
• forbidden[i] consists only of lowercase English letters.

## Solutions

• class Solution {
public int longestValidSubstring(String word, List<String> forbidden) {
var s = new HashSet<>(forbidden);
int ans = 0, n = word.length();
for (int i = 0, j = 0; j < n; ++j) {
for (int k = j; k > Math.max(j - 10, i - 1); --k) {
if (s.contains(word.substring(k, j + 1))) {
i = k + 1;
break;
}
}
ans = Math.max(ans, j - i + 1);
}
return ans;
}
}

• class Solution {
public:
int longestValidSubstring(string word, vector<string>& forbidden) {
unordered_set<string> s(forbidden.begin(), forbidden.end());
int ans = 0, n = word.size();
for (int i = 0, j = 0; j < n; ++j) {
for (int k = j; k > max(j - 10, i - 1); --k) {
if (s.count(word.substr(k, j - k + 1))) {
i = k + 1;
break;
}
}
ans = max(ans, j - i + 1);
}
return ans;
}
};

• class Solution:
def longestValidSubstring(self, word: str, forbidden: List[str]) -> int:
s = set(forbidden)
ans = i = 0
for j in range(len(word)):
for k in range(j, max(j - 10, i - 1), -1):
if word[k : j + 1] in s:
i = k + 1
break
ans = max(ans, j - i + 1)
return ans


• func longestValidSubstring(word string, forbidden []string) (ans int) {
s := map[string]bool{}
for _, x := range forbidden {
s[x] = true
}
n := len(word)
for i, j := 0, 0; j < n; j++ {
for k := j; k > max(j-10, i-1); k-- {
if s[word[k:j+1]] {
i = k + 1
break
}
}
ans = max(ans, j-i+1)
}
return
}

func max(a, b int) int {
if a > b {
return a
}
return b
}

• function longestValidSubstring(word: string, forbidden: string[]): number {
const s: Set<string> = new Set(forbidden);
const n = word.length;
let ans = 0;
for (let i = 0, j = 0; j < n; ++j) {
for (let k = j; k > Math.max(j - 10, i - 1); --k) {
if (s.has(word.substring(k, j + 1))) {
i = k + 1;
break;
}
}
ans = Math.max(ans, j - i + 1);
}
return ans;
}