var arr = [[1,2,3,4,5],
           [6,7,8,9,10],
           [11,12,13,14,15],
           [16,17,18,19,20],
           [21,22,23,24,25]]

就這么一個二維數組，如何從 arr[0][0]開始從外圈順時針旋轉輸出每一個數字？

//快速生成 n*n 的二維數組
let arr = [];
let num = 6;
for(let i=0;i<num*num;i++){
    let index = parseInt(i/num);
    if(!arr[index]){
        arr[index] = [];
    }
    arr[index][i%num] = i;
}

//算法
    order(arr){
        let rs = [];
        
        //邊長
        let length = arr[0].length;

        //圈數
        let circle = 0;

        //四個方向 right down left top
        let direction = ['r','d','l','t'];

        //用這個參數控制方向
        let dir_index = 0;

        //計數器
        let counts = 0;


        // x y 坐標
        let x = 0;
        let y = 0;

        while(true){
            let shouleCounts = length - 1 - circle*2;


            if(rs.length >= length*length){
                break;
            }

            //每圈的開始主動把第一個元素放進來
            if(counts == 0){
                
                x = circle;
                y = circle;
                rs.push(arr[x][y]);
                console.log(x,y);
                y++;
                counts++;

                continue;
            }


            //基數行最后一圈特殊，只有一個元素，放進來結束掉
            if(length%2 == 1 &&  circle == (length+1)/2){
                rs.push(arr[circle-1][circle-1]);
                break;
            }

            //控制方向
            if(counts%shouleCounts == 0 || counts == shouleCounts*4-1){
                dir_index++;
                if(dir_index == 4){
                    dir_index = 0;
                }
            }

            
            console.log(x,y);

            rs.push(arr[x][y]);


            //添加完后，開始變化坐標
            if(direction[dir_index] == 'r'){
                y++;
            }else if(direction[dir_index] == 'd'){
                x++;
            }else if(direction[dir_index] == 'l'){
                y--;
            }else if(direction[dir_index] == 't'){
                x--;
            }

            



            //控制每圈的循環次數，循環完畢后重置數據，進入下一圈循環
            if(counts == 4*shouleCounts-1){
                counts = 0;
                circle++;
            }


            //第一個元素要特殊處理，特殊處理中已經 count++
            if(counts>0){
                counts++;
            }
        }


        return rs;
    }