[LeetCode]Spiral Matrix

题目描述:

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].

解题思路：

class Solution {
public:
    vector<int> spiralOrder(vector<vector<int>>& matrix) {
        vector<int> result;
        if (matrix.size() == 0) {
            return result;
        }
        int left = 0;
        int right = matrix[0].size() - 1;
        int up = 0;
        int down = matrix.size() - 1;
        
        int n = matrix.size() * matrix[0].size();
        
        while (true) {
            for (int i = left; i <= right; ++i) {
                result.push_back(matrix[up][i]);
                --n;
            }
            if (n <= 0) {
                break;
            }
            
            up += 1;
            for (int i = up; i <= down; ++i) {
                result.push_back(matrix[i][right]);
                --n;
            }
            if (n <= 0) {
                break;
            }
            
            right -= 1;
            for (int i = right; i >= left; --i) {
                result.push_back(matrix[down][i]);
                --n;
            }
            if (n <= 0) {
                break;
            }
        
            down -= 1;
            for (int i = down; i >= up; --i) {
                result.push_back(matrix[i][left]);
                --n;
            }
            left += 1;
            
            if (n <= 0) {
                break;
            }
        }
        
        return result;
    }
};