LeetCode 2185. Counting Words With a Given Prefix Solution in Java, C++, Python & More | Explanation + Code

Description

You are given an array of strings words and a string pref.

Return the number of strings in words that contain pref as a prefix.

A prefix of a string s is any leading contiguous substring of s.

 

Example 1:

Input: words = ["pay","attention","practice","attend"], pref = "at"
Output: 2
Explanation: The 2 strings that contain "at" as a prefix are: "attention" and "attend".

Example 2:

Input: words = ["leetcode","win","loops","success"], pref = "code"
Output: 0
Explanation: There are no strings that contain "code" as a prefix.

 

Constraints:

• 1 <= words.length <= 100
• 1 <= words[i].length, pref.length <= 100
• words[i] and pref consist of lowercase English letters.

Solutions

Solution 1

PythonJavaC++GoTypeScriptRustC

class Solution: def prefixCount(self, words: List[str], pref: str) -> int: return sum(w.startswith(pref) for w in words)(code-box)

class Solution { public int prefixCount(String[] words, String pref) { int ans = 0; for (String w : words) { if (w.startsWith(pref)) { ++ans; } } return ans; } }(code-box)

class Solution { public: int prefixCount(vector<string>& words, string pref) { int ans = 0; for (auto& w : words) ans += w.find(pref) == 0; return ans; } };(code-box)

func prefixCount(words []string, pref string) (ans int) { for _, w := range words { if strings.HasPrefix(w, pref) { ans++ } } return }(code-box)

function prefixCount(words: string[], pref: string): number { return words.reduce((r, s) => (r += s.startsWith(pref) ? 1 : 0), 0); }(code-box)

impl Solution { pub fn prefix_count(words: Vec<String>, pref: String) -> i32 { words.iter().filter(|s| s.starts_with(&pref)).count() as i32 } }(code-box)

int prefixCount(char** words, int wordsSize, char* pref) { int ans = 0; int n = strlen(pref); for (int i = 0; i < wordsSize; i++) { if (strncmp(words[i], pref, n) == 0) { ans++; } } return ans; }(code-box)

Solution 2

PythonJavaC++Go

class Trie: def __init__(self): self.children = [None] * 26 self.cnt = 0 def insert(self, w): node = self for c in w: i = ord(c) - ord('a') if node.children[i] is None: node.children[i] = Trie() node = node.children[i] node.cnt += 1 def search(self, pref): node = self for c in pref: i = ord(c) - ord('a') if node.children[i] is None: return 0 node = node.children[i] return node.cnt class Solution: def prefixCount(self, words: List[str], pref: str) -> int: tree = Trie() for w in words: tree.insert(w) return tree.search(pref)(code-box)

class Trie { private Trie[] children = new Trie[26]; private int cnt; public void insert(String w) { Trie node = this; for (int i = 0; i < w.length(); ++i) { int j = w.charAt(i) - 'a'; if (node.children[j] == null) { node.children[j] = new Trie(); } node = node.children[j]; ++node.cnt; } } public int search(String pref) { Trie node = this; for (int i = 0; i < pref.length(); ++i) { int j = pref.charAt(i) - 'a'; if (node.children[j] == null) { return 0; } node = node.children[j]; } return node.cnt; } } class Solution { public int prefixCount(String[] words, String pref) { Trie tree = new Trie(); for (String w : words) { tree.insert(w); } return tree.search(pref); } }(code-box)

class Trie { public: Trie() : children(26) , cnt(0) {} void insert(string w) { Trie* node = this; for (auto& c : w) { int i = c - 'a'; if (!node->children[i]) { node->children[i] = new Trie(); } node = node->children[i]; ++node->cnt; } } int search(string pref) { Trie* node = this; for (auto& c : pref) { int i = c - 'a'; if (!node->children[i]) { return 0; } node = node->children[i]; } return node->cnt; } private: vector<Trie*> children; int cnt; }; class Solution { public: int prefixCount(vector<string>& words, string pref) { Trie* tree = new Trie(); for (auto& w : words) { tree->insert(w); } return tree->search(pref); } };(code-box)

type Trie struct { children [26]*Trie cnt int } func newTrie() *Trie { return &Trie{} } func (this *Trie) insert(w string) { node := this for _, c := range w { c -= 'a' if node.children[c] == nil { node.children[c] = newTrie() } node = node.children[c] node.cnt++ } } func (this *Trie) search(pref string) int { node := this for _, c := range pref { c -= 'a' if node.children[c] == nil { return 0 } node = node.children[c] } return node.cnt } func prefixCount(words []string, pref string) int { tree := newTrie() for _, w := range words { tree.insert(w) } return tree.search(pref) }(code-box)