Given an input string and a pattern, check if characters in the input string follows the same order as determined by characters present in the pattern. Assume there won’t be any duplicate characters in the pattern.
Input: string = "engineers rock", pattern = "er"; Output: true All 'e' in the input string are before all 'r'. Input: string = "engineers rock", pattern = "egr"; Output: false There are two 'e' after 'g' in the input string. Input: string = "engineers rock", pattern = "gsr"; Output: false There are one 'r' before 's' in the input string.
We have discussed two approaches to solve this problem.
Check if string follows order of characters defined by a pattern or not | Set 1
Check if string follows order of characters defined by a pattern or not | Set 2
In this approach we first assign a label (or order) to characters of pattern. The labels are assigned in increasing order.
For example, the pattern “gsr” is labeled as following
"g" => 1 "s" => 2 "r" => 3
It means ‘g’ will come first, then ‘s’, then ‘r’
After assigning labels to pattern characters, we iterate through string characters. While traversing, we keep track of label (or order) of last visited character. If label of current character is less than previous character, we return false. Otherwise we update last label. If all characters follow order, we return true.
Below is the C++ implementation
Time Complexity of this program is O(n) with constant extra space (the array label is of constant size, 256).
This article is contributed by Mohammed Iftekharul Islam Rupam. If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to email@example.com. See your article appearing on the GeeksforGeeks main page and help other Geeks.
Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above.
- Return maximum occurring character in an input string
- Print all the duplicates in the input string
- Remove characters from the first string which are present in the second string
- Remove duplicates from a given string
- A Program to check if strings are rotations of each other or not
- Print reverse of a string using recursion
- Write a program to print all permutations of a given string
- Divide a string in N equal parts
- Given a string, find its first non-repeating character
- Write a program to reverse an array or string
- Print list items containing all characters of a given word
- Check for balanced parentheses in an expression
- Reverse words in a given string
- Find the smallest window in a string containing all characters of another string
- Naive algorithm for Pattern Searching