10000 reverse alphabetical chars from a string · developgo/algorithms_with_Go@48e8104 · GitHub
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reverse alphabetical chars from a string
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‎README.md

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@@ -107,7 +107,7 @@ WIP, the description of the below `unsolved yet` problems can be found in the or
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## [String / Array](https://github.com/danrusei/algorithms_with_Go/tree/main/strings)
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- [] Reverse an array without affecting special characters
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- [x] [Reverse an array without affecting special characters](https://github.com/danrusei/algorithms_with_Go/tree/main/strings/reverse_alpha)
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- [] All Possible Palindromic Partitions
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- [] Count triplets with sum smaller than a given value
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- [] Convert array into Zig-Zag fashion
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- [] Find the smallest positive integer value that cannot be represented as sum of any subset of a given array
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- [] Smallest subarray with sum greater than a given value
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- [] Stock Buy Sell to Maximize Profit
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‎strings/reverse_alpha/README.md

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# Reverse a string without affecting special characters
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Given a string, that contains special character together with alphabets (‘a’ to ‘z’ and ‘A’ to ‘Z’), reverse the string in a way that special characters are not affected.
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## Example
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> Input: str = "a,b$c"
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> Output: str = "c,b$a"
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> Note that $ and , are not moved anywhere.
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> Only subsequence "abc" is reversed
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>
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> Input: str = "Ab,c,de!$"
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> Output: str = "ed,c,bA!$"
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## Algorithm
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* Let input string be `str` and length of string be `n`
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* l = 0, r = n-1
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* for `l` is smaller than `r`, do following
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* If `str[l]` is not an alphabetic character, do `l++`
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* else if `str[r]` is not an alphabetic character, do `r--`
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* else swap `str[l]` and `str[r]`
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## Result
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```bash
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$ go test -v
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=== RUN TestReverse
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=== RUN TestReverse/simple
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=== RUN TestReverse/with_punctuation
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=== RUN TestReverse/with_capital
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=== RUN TestReverse/with_trailing_space
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--- PASS: TestReverse (0.00s)
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--- PASS: TestReverse/simple (0.00s)
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--- PASS: TestReverse/with_punctuation (0.00s)
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--- PASS: TestReverse/with_capital (0.00s)
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--- PASS: TestReverse/with_trailing_space (0.00s)
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PASS
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ok _/home/rdan/projects_public/algorithms_with_Go/strings/reverse_alpha 0.001s
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```

‎strings/reverse_alpha/reverse.go

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package reverse
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import (
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"fmt"
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"unicode"
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)
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func reverse(input string) string {
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toSlice := make([]rune, len(input))
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for i, c := range input {
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toSlice[i] = c
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}
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reverseSlice(toSlice)
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return fmt.Sprint(string(toSlice))
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}
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func reverseSlice(input []rune) {
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l := 0
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r := len(input) - 1
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for l < r {
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if !unicode.IsLetter(input[l]) {
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l++
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} else if !unicode.IsLetter(input[r]) {
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r--
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} else {
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input[l], input[r] = input[r], input[l]
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l++
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r--
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}
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}
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}

‎strings/reverse_alpha/reverse_test.go

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package reverse
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import "testing"
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func TestReverse(t *testing.T) {
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for _, tc := range testcases {
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t.Run(tc.name, func(t *testing.T) {
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result := reverse(tc.input)
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if result != tc.output {
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t.Errorf("Expected: %s, got: %s", tc.output, result)
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}
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})
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}
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}

‎strings/reverse_alpha/test_cases.go

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package reverse
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var testcases = []struct {
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name string
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input string
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output string
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}{
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{
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name: "simple",
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input: "abc",
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output: "cba",
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},
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{
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name: "with_punctuation",
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input: "a,b$c",
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output: "c,b$a",
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},
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{
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name: "with_capital",
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input: "Ab,c,de!$",
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output: "ed,c,bA!$",
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},
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{
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name: "with_trailing_space",
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input: "a,b$c ",
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output: "c,b$a ",
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},
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}

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