reverse_words_string_test.go

/*
Problem:
- Given a string, reverse it word by word.

Example:
- Input: "hard so be to have not does interview coding"
  Output: "coding interview does not have to be so hard"

Approach:
- Approach with a two-pass solution.
- The first pass is to split the string into an array of words separated by
  spaces.
- The second pass is to reverse the order of words in the array by using
  two-pointer approach: swap two values on both ends as we move toward the
  middle.
- Concatenate the values of ordered array to create a final string.

Cost:
- O(n) time, O(n) space.
*/

package leetcode

import (
	"strings"
	"testing"

	"github.com/hoanhan101/algo/common"
)

func TestReverseWordsString(t *testing.T) {
	tests := []struct {
		in       string
		expected string
	}{
		{"", ""},
		{"a", "a"},
		{" a", "a"},
		{"a ", "a"},
		{"b a", "a b"},
		{"c b a", "a b c"},
		{"d c b a", "a b c d"},
		{"hard so be to have not does interview coding", "coding interview does not have to be so hard"},
	}

	for _, tt := range tests {
		result := reverseWordsString(tt.in)
		common.Equal(t, tt.expected, result)
	}
}

func reverseWordsString(in string) string {
	// if the input is an empty string, return itself.
	if in == "" {
		return in
	}

	// slice input string into a list of words separated by spaces.
	words := strings.Split(in, " ")

	// clean up leading and trailing space if there is any.
	if words[0] == "" {
		words = words[1:]
	}

	if words[len(words)-1] == "" {
		words = words[:len(words)-1]
	}

	// start reversing the order of words by first initializing the start and
	// end index pointer.
	start := 0
	end := len(words) - 1

	for start < end {
		// swap 2 character using a temp variable.
		common.SwapString(words, start, end)

		// move the cursor toward the middle.
		start++
		end--
	}

	// return the concatenated string created from words.
	return strings.Join(words, " ")
}