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Formatted question description: https://leetcode.ca/all/1961.html

1961. Check If String Is a Prefix of Array

Level

Easy

Description

Given a string s and an array of strings words, determine whether s is a prefix string of words.

A string s is a prefix string of words if s can be made by concatenating the first k strings in words for some positive k no larger than words.length.

Return true if s is a prefix string of words, or false otherwise.

Example 1:

Input: s = “iloveleetcode”, words = [“i”,”love”,”leetcode”,”apples”]

Output: true

Explanation: s can be made by concatenating “i”, “love”, and “leetcode” together.

Example 2:

Input: s = “iloveleetcode”, words = [“apples”,”i”,”love”,”leetcode”]

Output: false

Explanation:

It is impossible to make s using a prefix of arr.

Constraints:

• 1 <= words.length <= 100
• 1 <= words[i].length <= 20
• 1 <= s.length <= 1000
• words[i] and s consist of only lowercase English letters.

Solution

Loop over s and words. If the characters do not match, return false. If s finishes but the last character of s is not the last character of any of the word in words, return false. If s finishes at the last character of any of the word in words, return true.

• Java
• Python
• C++
• Go
• TypeScript

• class Solution {
      public boolean isPrefixString(String s, String[] words) {
          int length = s.length();
          int arrLength = words.length;
          int index = 0;
          for (int i = 0; i < arrLength && index < length; i++) {
              String word = words[i];
              int wordLength = word.length();
              int j = 0;
              while (j < wordLength && index < length) {
                  if (s.charAt(index) == word.charAt(j)) {
                      index++;
                      j++;
                  } else
                      return false;
              }
              if (index == length && j < wordLength)
                  return false;
          }
          return index == length;
      }
  }
  
  ############
  
  class Solution {
      public boolean isPrefixString(String s, String[] words) {
          StringBuilder t = new StringBuilder();
          for (String w : words) {
              t.append(w);
              if (s.length() == t.length()) {
                  return s.equals(t.toString());
              }
          }
          return false;
      }
  }
  

• class Solution:
      def isPrefixString(self, s: str, words: List[str]) -> bool:
          t = 0
          for i, w in enumerate(words):
              t += len(w)
              if len(s) == t:
                  return ''.join(words[: i + 1]) == s
          return False
  
  ############
  
  # 1961. Check If String Is a Prefix of Array
  # https://leetcode.com/problems/check-if-string-is-a-prefix-of-array/
  
  class Solution:
      def isPrefixString(self, s: str, words: List[str]) -> bool:
          ss = ""
          n = 0
          
          for word in words:
              n += len(word)
              ss += word
  
              if s[:n] != ss:
                  ss = ss[:n - len(word)]
                  return ss == s
              
          return ss == s
  
  

• class Solution {
  public:
      bool isPrefixString(string s, vector<string>& words) {
          string t = "";
          for (string& w : words) {
              t += w;
              if (t.size() == s.size()) return t == s;
          }
          return false;
      }
  };
  

• func isPrefixString(s string, words []string) bool {
  	t := ""
  	for _, w := range words {
  		t += w
  		if t == s {
  			return true
  		}
  	}
  	return false
  }
  

• function isPrefixString(s: string, words: string[]): boolean {
      const t: string[] = [];
      const n = s.length;
      let m = 0;
      for (const w of words) {
          m += w.length;
          if (m > n) {
              return false;
          }
          t.push(w);
          if (m === n) {
              return s === t.join('');
          }
      }
      return false;
  }
  
  

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