Mauritus national flag problem

Question

I\'ve made a solution for the Dutch national flag problem already.

But this time, I want to try something more difficult: the Mauritus national flag problem - 4 colours,

Answer 1

let a:string[] = ['1','2','1','0','2','4','3','0','1','3'];

function sort3(a:string[]):void{
    let low = 0;
    let mid1 = 0;
    let mid2 = 0;
    let mid3 = 0;
    let high = a.length - 1;
    while(mid3<=high){
        switch(a[mid3]){
            case '0': [a[mid3],a[low]] = [a[low],a[mid3]];
                    low++;
                    if(mid1 < low)
                    mid1++;
                    if(mid2 < mid1)
                    mid2++;
                    if(mid3 < mid2)
                    mid3++;
                    break;

            case '1': [a[mid3],a[mid1]] = [a[mid1],a[mid3]];
                    mid1++;
                    if(mid2 < mid1)
                    mid2++;
                    if(mid3 < mid2)
                    mid3++
                    break;

            case '2': [a[mid2],a[mid3]] = [a[mid3],a[mid2]];
                        mid2++;
                        mid3++;
                   break;

            case '3':
                    mid3++;break;

            case '4': [a[mid3],a[high]] = [a[high],a[mid3]];
                        high--;
        }
    }
}