[4]54. Spiral Matrix/59. Spiral Matrix II(Java)

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54. Spiral Matrix

---

Given a matrix of m x n elements (m rows, n columns), return all elements of the matrix in spiral order.

For example,
Given the following matrix:

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

You should return [1,2,3,6,9,8,7,4,5].

class Solution {
    public List<Integer> spiralOrder(int[][] matrix) {
        List<Integer> res = new ArrayList<>();
        if (matrix.length == 0) 
            return res;
        
        int rowBegin = 0, colBegin = 0;
        int rowEnd = matrix.length - 1;
        int colEnd = matrix[0].length - 1;
        
        while (rowBegin <= rowEnd && colBegin <= colEnd) {
            // Traverse right
            for (int j = colBegin; j <= colEnd; j ++) {
                res.add(matrix[rowBegin][j]);
            }
            rowBegin ++;
            // Traverse down
            for (int i = rowBegin; i <= rowEnd; i ++) {
                res.add(matrix[i][colEnd]);
            }
            colEnd --;
            if (rowBegin <= rowEnd) {
                // Traverse left
                for (int j = colEnd; j >= colBegin; j --) {
                    res.add(matrix[rowEnd][j]);
                }
                rowEnd --;
            }
            if (colBegin <= colEnd) {
                // Traverse up
                for (int i = rowEnd; i >= rowBegin; i --) {
                    res.add(matrix[i][colBegin]);
                }
                colBegin ++;
            }
        }
        return res;
    }
}

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 ]
]

class Solution {
    public int[][] generateMatrix(int n) {
        int[][] matrix = new int[n][n];
        if (n == 0) return matrix;        
        
        int rowBegin = 0, colBegin = 0;
        int rowEnd = n - 1, colEnd = n - 1;
        int num = 1;
        
        while (rowBegin <= rowEnd && colBegin <= colEnd) {
            // Traverse right
            for (int j = colBegin; j <= colEnd; j ++) {
                matrix[rowBegin][j] = num ++;
            }
            rowBegin ++;
            // Traverse down
            for (int i = rowBegin; i <= rowEnd; i ++) {
                matrix[i][colEnd] = num ++;
            }
            colEnd --;
            if (rowBegin <= rowEnd) {
                // Traverse left
                for (int j = colEnd; j >= colBegin; j --) {
                    matrix[rowEnd][j] = num ++;
                }
                rowEnd --;
            }
            if (colBegin <= colEnd) {
                // Traverse up
                for (int i = rowEnd; i >= rowBegin; i --) {
                    matrix[i][colBegin] = num ++;
                }
                colBegin ++;
            }
        }
        return matrix;
    }
}