프로그래머스 | 삼각달팽이

function solution(n) {
    let arr = [];
    
    for(let i=1;i<=n;i++){
        arr.push(Array.from({length:i},()=>0));
    }
    
    let col_s=0;
    let col_e=n-1;
    let row_s=0;
    let row_e=n-1;
    let num=1;
    let cnt=0;
    let step=1;
    for(let i=n;i>=1;i--){
        if(step===1){
            for(let a=row_s;a<=row_e;a++){
                arr[a][col_s]=num;
                num++
            }
            row_s+=1;
            col_s+=1;
        }
        else if(step===2){
            for(let b=col_s;b<=col_e;b++){
                arr[row_e][b]=num;
                num++
            }
            col_e-=1;
            row_e-=1;
        }
        
        else if(step===3){
            for(let c=row_e;c>=row_s;c--){
                arr[c][arr[c].length-1-cnt]=num
                num++
            }
            row_s+=1;
            col_e-=1
            cnt+=1
        }
        step++;
        if(step>3)step=1;
    }
    
    return arr.flat();
}