Leetcode-Spiral Matrix II

Given an integer n, generate a square matrix filled with elements from 1 to n² in spiral order.

For example,
Given n = 3,

You should return the following matrix:

[
 [ 1, 2, 3 ],
 [ 8, 9, 4 ],
 [ 7, 6, 5 ]
]

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Solution:

public class Solution {
    public int[][] generateMatrix(int n) {
        int[][] matrix = new int[n][n];

        int[] x = new int[]{0,1,0,-1};
        int[] y = new int[]{1,0,-1,0};      
        int direction = 0;
        int curX = 0, curY=0;        
        int rowStart = 0, rowEnd = n-1, colStart=0, colEnd=n-1;
        int len = n*n;
        
        for (int i=0;i<len;i++){
            matrix[curX][curY]=i+1;    
            int nextX = curX+x[direction];
            int nextY = curY+y[direction]; 
            //Determin the availability of next point.
            if (nextX>rowEnd || nextX<rowStart || nextY>colEnd || nextY<colStart){
                direction = (direction+1)%4;
                nextX = curX+x[direction];
                nextY = curY+y[direction];
                //Update the availability of rows and cols according the direction change.
                if (direction==1) rowStart++;
                if (direction==2) colEnd--;
                if (direction==3) rowEnd--;
                if (direction==0) colStart++;
            }
            curX = nextX;
            curY = nextY;
        }

        return matrix;

    }
}