[Codility] StrSymmetryPoint (Go)

https://app.codility.com/programmers/trainings/4/str_symmetry_point/

StrSymmetryPoint coding task - Practice Coding - Codility

 

Task description

 

Write a function:

func Solution(S string) int

 that, given a string S, returns the index (counting from 0) of a character such that the part of the string to the left of that character is a reversal of the part of the string to its right. The function should return −1 if no such index exists.

Note: reversing an empty string (i.e. a string whose length is zero) gives an empty string.

For example, given a string:

"racecar"

the function should return 3, because the substring to the left of the character "e" at index 3 is "rac", and the one to the right is "car".

Given a string:

"x"

the function should return 0, because both substrings are empty.

Write an efficient algorithm for the following assumptions:

• the length of string S is within the range [0..2,000,000].

---

package solution

import "strings"

func Solution(S string) int {
   	var ln = len([]rune(S))

	switch ln {
	case 0:
		return -1
	case 1:
		return 0
	}

	var mid = len([]rune(S)) / 2

	if S[0:mid+1] != getReverserStr(mid, S) {
		return -1
	}

	return mid
}

func getReverserStr(idx int, S string) string {

	var result strings.Builder

	for i := len([]rune(S)) - 1; i >= idx; i-- {
		result.WriteString(S[i : i+1])
	}

	return result.String()
}