1. Runtime Distribution

2. Submission Details

3. Description

Given a string which contains only lowercase letters, remove duplicate letters so that every letter appear once and only once. You must make sure your result is the smallest in lexicographical order among all possible results.

4. Example

Given "bcabc"
Return "abc"
Given "cbacdcbc"
Return "acdb"

5. Code

char* removeDuplicateLetters(char* s) {

    int remain_count[128];
    int result_has[128];

    for(int i = 97; i< 128; i++)
    {
        remain_count[i] = 0;
        result_has[i] = 0;
    }

    int length = strlen(s);

    for(int i = 0; i< length; i++)
    {
        remain_count[s[i]] ++;
    }

    char* stack = malloc(sizeof(char)*length);

    int top = 0;

    for(int i = 0; i< length; i++)
    {
        while(top > 0)
        {
            if(stack[top -1] < s[i] || remain_count[stack[top - 1]] == 0 || result_has[s[i]])
            {
                break;
            }
            result_has[stack[top - 1]] --;
            top--;
        }

        if(!result_has[s[i]])
        {
            stack[top++] = s[i];
            result_has[s[i]] ++;
        }

        remain_count[s[i]] --;
    }

    stack[top] = '\0';
    return stack;
}

#include <string.h>
#include <stdlib.h>
#include <stdio.h>

char* removeDuplicateLetters(char* s) {

    int remain_count[128];
    int result_has[128];

    for(int i = 97; i< 128; i++)
    {
        remain_count[i] = 0;
        result_has[i] = 0;
    }

    int length = strlen(s);

    for(int i = 0; i< length; i++)
    {
        remain_count[s[i]] ++;
    }

    char* stack = malloc(sizeof(char)*length);

    int top = 0;

    for(int i = 0; i< length; i++)
    {
        while(top > 0)
        {
            if(stack[top -1] < s[i] || remain_count[stack[top - 1]] == 0 || result_has[s[i]])
            {
                break;
            }
            result_has[stack[top - 1]] --;
            top--;
        }

        if(!result_has[s[i]])
        {
            stack[top++] = s[i];
            result_has[s[i]] ++;
        }

        remain_count[s[i]] --;
    }

    stack[top] = '\0';
    return stack;
}

int main()
{
    char *s = "abacb\0";
    char * result = removeDuplicateLetters(s);
    puts(result);
    system("pause");
    return 0;
}