54. 59. Spiral Matrix

1.

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].

vector<int> spiralOrder(vector<vector<int>>& matrix) {
    vector<int> ans;
    int m = matrix.size();
    if(m < 1)
        return ans;
    int n = matrix[0].size(), size = m*n, x1=0, x2=m-1, y1=0, y2=n-1, i, j, k=0;
    while(k < size)
    {
        for(i=y1; i<=y2; i++)
        {
            ans.push_back(matrix[x1][i]);
            k++;
        }
        for(i=x1+1; i<=x2; i++)
        {
            ans.push_back(matrix[i][y2]);
            k++;
        }
        for(i=y2-1; x2>x1 && i>=y1; i--)
        {
            ans.push_back(matrix[x2][i]);
            k++;
        }
        for(i=x2-1; y2>y1 && i>x1; i--)
        {
            ans.push_back(matrix[i][y1]);
            k++;
        }
        x1++; x2--; y1++; y2--;
    }
    return ans;
}

注意：

下面和左面的边，即第三个和第四个for循环，要加条件x2>x1和y2>y1，否则会有重复元素。

2.

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 ]
]

vector<vector<int>> generateMatrix(int n) {
    vector<vector<int>> ans(n, vector<int>(n, 0));
    int size = n*n, x1=0, x2=n-1, y1=0, y2=n-1, i, j, k=0;
    while(k < size)
    {
        for(i=y1; i<=y2; i++)
            ans[x1][i] = ++k;
        for(i=x1+1; i<=x2; i++)
            ans[i][y2] = ++k;
        for(i=y2-1; x2>x1 && i>=y1; i--)
            ans[x2][i] = ++k;
        for(i=x2-1; y2>y1 && i>x1; i--)
            ans[i][y1] = ++k;
        x1++; x2--; y1++; y2--;
    }
    return ans;
}