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spiral matrix

admin 11月 13, 2020 0

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

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

Solution

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public class  {
    public List<Integer> spiralOrder(int[][] matrix) {
        List<Integer> res = new ArrayList<Integer>();
        if(matrix == null || matrix.length==0) return res;
        int left = 0, right = matrix[0].length-1, top = 0, bottom = matrix.length-1;
        while(left <= right && top <= bottom) {
            
            for(int i=left; i<=right; i++) {
                res.add(matrix[top][i]);
            }
            top++;
            //向下
            for(int i=top; i<=bottom;i++) {
                res.add(matrix[i][right]);
            }
            right--;
            //向左
            if(top<=bottom) {
                for(int i=right; i>=left; i--) {
                    res.add(matrix[bottom][i]);
                }
            }
            bottom--;
            //向上
            if(left<=right) {
                for(int i=bottom;i>=top;i--) {
                    res.add(matrix[i][left]);
                }
            }
            left++;
        }
        return res;
    }
}
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