gistfile1.txt

package main

import (
	"fmt"
)

var before [26][26]bool
var used[26]bool

func filter(arr []string, j int) []string {
	result := []string{}
	for _, s := range arr {
		if len(s) > j {
			result = append(result, s)	
		}
	}
	return result
}

func order(arr []string, j int) {
	arr = filter(arr, j)
	if len(arr) == 0 {
		return
	}	
	
	p := 0
	for i := 1; i < len(arr); i++ {
		used[arr[i][j] - 'a'] = true
		if arr[i][j] != arr[i-1][j] {
			before[arr[i-1][j]-'a'][arr[i][j] - 'a'] = true
			order(arr[p:i], j+1)
			p = i
		}
	}
	order(arr[p:], j+1)
}

func topsort(u int, seen map[int]bool, result *[]string) {
	if seen[u] {
		return
	}
	for v := 0; v < 26; v++ {
		if before[v][u] {
			topsort(v, seen, result)
		}
	}
	seen[u] = true
	*result = append(*result, string('a' + u))
}


func main() {
	arr := []string{"xww", "wxyz", "wxyw", "ywx", "ywz"}
	order(arr, 0)
	seen := make(map[int]bool)
	result := make([]string, 0)
	
	for i := 25; i >= 0; i-- {
		if used[i] {
			topsort(i, seen, &result)
		}
	}
	
	fmt.Println(result)
}