54. Spiral Matrix

Posted 2020-08-09 Machelsky

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].

思路：

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

step 1: add top line- from left to right
step 2: add right line - from top to bottom
step 3: add bottom line - from right to left
step 4 : add left line - from bottom to top 

注意边界条件: [2 3] 1.用总个数来限制，calling method会增加复杂度2.用 top bottom left right关系来限制
Solution 1:

public class Solution {
    public List<Integer> spiralOrder(int[][] matrix) {
        List<Integer> res=new ArrayList<Integer>();
        if(matrix==null||matrix.length==0)
        {
            return res;
        }
        int l=matrix[0].length;
        int h=matrix.length;
        int total=l*h;
        int left=0,top=0,right=l-1,bottom=h-1;
        while(res.size()<total)
        {
        for(int i=left;i<=right;i++)
        {
            res.add(matrix[top][i]);
        }
        top++;
        if(res.size()<total)
        {
        for(int j=top;j<=bottom;j++)
        {
            res.add(matrix[j][right]);
        }
        right--;
        }
        if(res.size()<total)
        {
        for(int k=right;k>=left;k--)
        {
            res.add(matrix[bottom][k]);
        }
        bottom--;
        }
        if(res.size()<total)
        {
        for(int m=bottom;m>=top;m--)
        {
            res.add(matrix[m][left]);
        }
        left++;
        }
        }
        return res;
    }
}

Solution2:

public class Solution {
    public List<Integer> spiralOrder(int[][] matrix) {
        List<Integer> res=new ArrayList<Integer>();
        if(matrix==null||matrix.length==0)
        {
            return res;
        }
        int l=matrix[0].length;
        int h=matrix.length;
        int total=l*h;
        int left=0,top=0,right=l-1,bottom=h-1;
        while(res.size()<total)
        {
        for(int i=left;i<=right;i++)
        {
            res.add(matrix[top][i]);
        }
        top++;
        if(top>bottom)
        {
            break;
        }
        for(int j=top;j<=bottom;j++)
        {
            res.add(matrix[j][right]);
        }
        right--;
        
        if(right<left)
        {
            break;
        }
        for(int k=right;k>=left;k--)
        {
            res.add(matrix[bottom][k]);
        }
        bottom--;
    
        if(bottom<top)
        {
            break;
        }
        for(int m=bottom;m>=top;m--)
        {
            res.add(matrix[m][left]);
        }
        left++;
        
        }
        return res;
    }
}