Write a program to find increasing decreasing string

Published: June 7, 2022Last updated: June 7, 2022code, program, string

Program description:

You are given a string s. Reorder the string using the following algorithm:

Pick the smallest character from s and append it to the result.
Pick the smallest character from s which is greater than the last appended character to the result and append it.
Repeat step 2 until you cannot pick more characters.
Pick the largest character from s and append it to the result.
Pick the largest character from s which is smaller than the last appended character to the result and append it.
Repeat step 5 until you cannot pick more characters.
Repeat the steps from 1 to 6 until you pick all characters from s.
In each step, If the smallest or the largest character appears more than once you can choose any occurrence and append it to the result.

Return the result string after following this algorithm.

Example #1:

Input: s = "aaaabbbbcccc"
Output: "abccbaabccba"
Explanation: After steps 1, 2 and 3 of the first iteration, result = "abc"
After steps 4, 5 and 6 of the first iteration, result = "abccba"
First iteration is done. Now s = "aabbcc" and we go back to step 1
After steps 1, 2 and 3 of the second iteration, result = "abccbaabc"
After steps 4, 5 and 6 of the second iteration, result = "abccbaabccba"

Example #2:

Input: s = "upokary"
Output: "akopruy"
Explanation: 
Explanation: The word "upokary" becomes "akopruy" after re-ordering it with the mentioned algorithm.

Problem solution:

    const sortString = (s) => {
        const len = s.length;
        const freq = [];

        for (let index = 0; index < len; index++) {
            const key = s.charCodeAt(index) - 97;
            freq[key] = freq[key] ? freq[key] + 1: 1;
        }

        let output = '';
        let count = 0;
        while (count < len) {
            for (let i = 0; i < 26; i++) {
                if (freq[i] > 0) {
                    output += String.fromCharCode(i+97);
                    freq[i] = freq[i] - 1;
                    count++;
                }
            }

            for (let i = 25; i >= 0; i--) {
                if (freq[i] > 0) {
                    output += String.fromCharCode(i+97);
                    freq[i] = freq[i] - 1;
                    count++;
                }
            }
        }
        return output;
    }


    const str = 'upokary';
    console.log(sortString(str)); // akopruy

Program description:

Example #1:

Example #2:

Problem solution:

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