LeetCode //C - 290. Word Pattern
290. Word Pattern
Given a pattern and a string s, find if s follows the same pattern.
Here follow means a full match, such that there is a bijection between a letter in pattern and a non-empty word in s.
Example 1:
Input: pattern = “abba”, s = “dog cat cat dog”
Output: true
Example 2:
Input: pattern = “abba”, s = “dog cat cat fish”
Output: false
Example 3:
Input: pattern = “aaaa”, s = “dog cat cat dog”
Output: false
Constraints:
- 1 <= pattern.length <= 300
- pattern contains only lower-case English letters.
- 1 <= s.length <= 3000
- s contains only lowercase English letters and spaces ’ '.
- s does not contain any leading or trailing spaces.
- All the words in s are separated by a single space.
From: LeetCode
Link: 290. Word Pattern
Solution:
Ideas：
The code for the wordPattern function is designed to determine whether a given string s follows a specific pattern. Here’s a breakdown of the idea behind the code:
-
Initialization: The code initializes an array of pointers words, where each index corresponds to a lowercase letter in the pattern (from ‘a’ to ‘z’). This array will be used to track the mapping between each character in the pattern and a corresponding word in the string s.
-
String Copy: Since the code utilizes strtok to tokenize the string s, which alters the original string, a copy of the string is made to preserve the input.
-
Tokenization and Mapping: The code tokenizes the string s into words and iterates through these words alongside the characters in the pattern:
- If the pattern is exhausted before all words are processed, the function returns false, as there is a mismatch in length.
- For each character in the pattern, the code checks whether it has been mapped to a word before. If not, it verifies that no other character has been mapped to the current word (to ensure a bijection). If all is well, the current character is mapped to the current word.
- If the character has already been mapped to a word, the code checks that this word matches the current word in the string. If there’s a mismatch, the function returns false.
-
Length Check: After processing all words, the code checks whether the pattern’s length matches the number of words. If there’s a mismatch, the function returns false.
-
Result: If all checks pass, the function returns true, indicating that the string s follows the given pattern.
Code:
bool wordPattern(char * pattern, char * s) {char *words[26];for (int i = 0; i < 26; i++) words[i] = NULL;char *s_copy = strdup(s);char *token = strtok(s_copy, " ");int i = 0;while (token != NULL) {// If the pattern is shorter than the number of words, return falseif (i >= strlen(pattern)) {free(s_copy);return false;}int idx = pattern[i] - 'a';if (words[idx] == NULL) {// Check if any other character maps to the same wordfor (int j = 0; j < 26; j++) {if (words[j] && strcmp(words[j], token) == 0) {free(s_copy);return false;}}words[idx] = token;} else {if (strcmp(words[idx], token) != 0) {free(s_copy);return false; // Mismatch in mapping}}token = strtok(NULL, " ");i++;}free(s_copy);// Check if pattern length matches the number of wordsif (i != strlen(pattern)) return false;return true;
}