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.
Another solution to the same problem is posted here.
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.
The idea here is to reduce the given string to the pattern given. For characters given in the pattern, we only keep the corresponding characters in the string. In the new string, we delete continuous repeated characters. The modified string should then be equal to the pattern given. Lastly, we compare modified string to the pattern given and return true of false accordingly.
str = "bfbaeadeacc", pat = "bac" 1) Remove extra characters from str (characters that are not present in pat str = "bbaaacc" [f, e and d are removed] 3) Removed consecutive repeating occurrences of characters str = "bac" 4) Since str is same as pat, we return true
Below is implementation of above steps.
Expected: true, Actual: true Expected: false, Actual: false Expected: false, Actual: false Expected: true, Actual: true
Time Complexity: Time complexity of above implementations is actually O(mn + n^2) as we use deleteCharAt() to remove characters. We can optimize above solution to work in linear time. Instead of using deleteCharAr(), we can create an empty string and add only required characters to it.
StringBuilder is used to operate on input string. This is because StringBuilder is mutable, while String is immutable object. To create a new string takes O(n) space, so extra space is O(n).
We have discussed two more 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 3
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Improved By : sanjeev2552