Solution.java

public class Solution {
    public int[][] generateMatrix(int n) {
        int[][] res = new int[n][n];
        int left = 0;
        int right = n - 1;
        int top = 0;
        int bottom = n - 1;
        int count = 0;

        while(count < n * n) {
            for (int i = left; i <= right && count < n*n; i++) {
                res[top][i] = ++count;
            }
            for (int i = top + 1; i < bottom && count < n*n; i++) {
                res[i][right] = ++count;
            }
            for (int i = right; i >= left && count < n*n; i--) {
                res[bottom][i] = ++count;
            }
            for (int i = bottom - 1; i > top && count < n*n; i--) {
                res[i][left] = ++count;
            }
            left++;
            right--;
            top++;
            bottom--;
        }
        return res;
    }
}