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Program.cs
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Program.cs
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using System;
using System.Collections.Generic;
namespace RemoveDuplicateLetters
{
class Program
{
static void Main(string[] args)
{
Console.WriteLine("Hello World!");
}
static string RemoveDuplicateLetters(string s)
{
var record = new int[26];
foreach (var letter in s)
record[letter - 'a']++;
var stack = new Stack<char>();
foreach (var letter in s)
{
record[letter - 'a']--;
if(stack.Contains(letter)) continue;
while (stack.Count != 0 && letter < stack.Peek() && record[stack.Peek() - 'a'] > 0)
stack.Pop();
stack.Push(letter);
}
var res = "";
while (stack.Count != 0)
res = stack.Pop() + res;
return res;
}
}
}