Problem
Given a positive integer n, generate a square matrix filled with elements from 1 to n2 in spiral order.
Example:
Input: 3
Output:
[
[ 1, 2, 3 ],
[ 8, 9, 4 ],
[ 7, 6, 5 ]
]
Solution
/**
* @param {number} n
* @return {number[][]}
*/
var generateMatrix = function(n) {
var x1 = 0;
var x2 = n - 1;
var y1 = 0;
var y2 = n - 1;
var i = 0;
var res = Array(n).fill(0).map(_ => Array(n));
while (x1 <= x2 && y1 <= y2) {
for (var x = x1; x <= x2; x++) res[y1][x] = ++i;
for (var y = y1 + 1; y <= y2; y++) res[y][x2] = ++i;
for (var x = x2 - 1; x > x1; x--) res[y2][x] = ++i;
for (var y = y2; y > y1; y--) res[y][x1] = ++i;
x1++;
x2--;
y1++;
y2--;
}
return res;
};
Explain:
绕圈，1 => 2 => 3 => 4 => 5
111
452
432
Complexity:
- Time complexity : O(n^2).
- Space complexity : O(n^2).