[Algorithm] Print 2-D array in spiral order

 

The idea to solve the problem is set five variable, first direction, we need to switch direction after we finish printing one row or one column.

dir = (dir+1) % 4

 

Then set four boundry, top, left, right, bottom:

  let results = [],
        dir = 0, //0: left -> right, 1: top -> bottom, 2: right -> left, 3: bottom -> top
        top = 0,
        bottom = arys.length - 1,
        left = 0,
        right = arys[0].length - 1;

Each time finish printing a row or a column, modify the boundry accordingly:

function PrintSpiralOrder (arys) {
  let results = [],
        dir = 0, //0: left -> right, 1: top -> bottom, 2: right -> left, 3: bottom -> top
        top = 0,
        bottom = arys.length - 1,
        left = 0,
        right = arys[0].length - 1;
  
  while (top <= bottom && left <= right) {
     if (dir === 0) {
       for (let i = left; i <= right; i++) {
         results.push(arys[top][i]);
       }
       top++;
     } else if (dir === 1) {
       for (let i = top; i <= bottom; i++) {
         results.push(arys[i][right]);
       }
       right--;
     } else if (dir === 2) {
       for (let i = right; i >= left; i--) {
         results.push(arys[bottom][i]);
       }
       bottom--;
     } else if (dir === 3) {
       for (let i = bottom; i >= top; i--) {
         results.push(arys[i][left]);
       }
       left++;
     }
    
     dir = (dir + 1) % 4;
  }
  
  return results;
}

const data = [
  [2,4,6,8],
  [5,9,12,16],
  [2,11,5,9],
  [3,2,1,8]
];

const res = PrintSpiralOrder(data);
console.log(res); // [ 2, 4, 6, 8, 16, 9, 8, 1, 2, 3, 2, 5, 9, 12, 5, 11 ]