ReverseShuffleMerge.js

'use strict';

const fs = require('fs');

process.stdin.resume();
process.stdin.setEncoding('utf-8');

let inputString = '';
let currentLine = 0;

process.stdin.on('data', inputStdin => {
    inputString += inputStdin;
});

process.stdin.on('end', _ => {
    inputString = inputString.replace(/\s*$/, '')
        .split('\n')
        .map(str => str.replace(/\s*$/, ''));

    main();
});

function readLine() {
    return inputString[currentLine++];
}

// Complete the reverseShuffleMerge function below.
function reverseShuffleMerge(s) {
let map={};
    s = s.split('').reverse('').join('')
    for(let item of s.split('')){
        map[item]=map[item]?map[item]+1:1;
    }
    let ref={}
    for(let key in map){
        ref[key] = map[key]/2
    }
    let solution = [],i=0;
    while (solution.length<s.length/2){
        let min_char_pos = -1
        //find the smallest
        //find the smallest
        //find the smallest
        while(true){
            let c=s[i];
            if(ref[c]>0&&(min_char_pos<0||c<s[min_char_pos])){
                min_char_pos = i;
            }
            map[c] -= 1;
            if(map[c] < ref[c]){
                break
            }
            i+=1
        }
        //found the one, restore the count of other
        for(let j=min_char_pos+1;j<i+1;j++){
            map[s[j]]+=1
        }
        //find the smallest
        //find the smallest
        //find the smallest
        ref[s[min_char_pos]]-=1
        solution.push(s[min_char_pos]);
        i= min_char_pos+1
    }
    return solution.join('');

}

function main() {
    const ws = fs.createWriteStream(process.env.OUTPUT_PATH);

    const s = readLine();

    let result = reverseShuffleMerge(s);

    ws.write(result + "\n");

    ws.end();
}