59. 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 ]
]

public class Solution {
    public int[][] generateMatrix(int n) {
        int startx = 0,starty = 0,endx = n-1,endy = n-1;
        int[][] ans = new int[n][n];
        int count = 1;
        while(startx <= endx && starty <= endy){
            for(int i = startx;i<=endx;i++){
                ans[starty][i] = count++;
            }
            starty++;
            
            for(int i = starty;i<=endy;i++){
                ans[i][endx] = count++;
            }
            endx--;
            
            for(int i = endx;i>=startx;i--){
                ans[endy][i] = count++;
            }
            endy--;
            
            for(int i = endy;i>=starty;i--){
                ans[i][startx] = count++;
            }
            startx++;
        }
        return ans;
    }
}

class Solution {
    public int[][] generateMatrix(int n) {
        int left = 0, right = n-1, top = 0, bottom = n-1;
        int counter = 0;
        int[][] res = new int[n][n];
        while(top <= bottom && left <= right){
            for(int i=left; i<=right; i++){
                res[top][i] = ++counter;
            }
            top++;
            for(int i=top; i<=bottom; i++){
                res[i][right] = ++counter;
            }
            right--;
            for(int i=right; i>=left; i--){
                res[bottom][i] = ++counter;
            }
            bottom--;
            for(int i=bottom; i>=top; i--){
                res[i][left] = ++counter;
            }
            left++;
        }
        return res;
    }
}

class Solution {
    public int[][] generateMatrix(int n) {
        int totItr = 2 * n - 1;
        int[][] mat = new int[n][n];

        int startRow = 0;
        int endRow = n - 1;
        int startCol = 0;
        int endCol = n - 1;
        int count = 1;
        for (int i = 0; i < totItr; i++) {
            for (int j = startCol; j <= endCol; j++) {
                mat[startRow][j] = count++;
            }
            startRow++;

            for (int j = startRow; j <= endRow; j++) {
                mat[j][endCol] = count++;
            }
            
            endCol--;
            
            for(int j = endCol; j>= startCol; j--) {
                mat[endRow][j] = count++;
            }
            
            endRow--;
            
            for(int j = endRow; j>= startRow; j--) {
                mat[j][startCol] = count++;
            }
            
            startCol++;
        }
        
        return mat;
    }
}