54.Spiral Matrix

Tags: Medium Array

Links: https://leetcode.com/problems/spiral-matrix/

---

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

Example 1:

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

Example 2:

Input:
[
  [1, 2, 3, 4],
  [5, 6, 7, 8],
  [9,10,11,12]
]
Output: [1,2,3,4,8,12,11,10,9,5,6,7]

---

class Solution {
public:
    vector<int> spiralOrder(vector<vector<int>>& matrix) {
        std::ios_base::sync_with_stdio(false);
        cin.tie(NULL);
        cout.tie(NULL);

        int m = matrix.size();
        if (m == 0) return {};
        int n = matrix[0].size();

        vector<int> res(m * n);
        int row = 0, col = 0;
        int cnt = 0;
        int direction = 0;

        while (cnt < m * n) {
            res[cnt++] = matrix[row][col];
            matrix[row][col] = INT_MAX;

            while (cnt < m * n) {
                if (direction == 0) {
                    if (col + 1 < n && matrix[row][col + 1] != INT_MAX) {
                        ++col; break;
                    }
                    else {
                        direction = (direction + 1) % 4;
                    }
                }
                if (direction == 1) {
                    if (row + 1 < m && matrix[row + 1][col] != INT_MAX) {
                        ++row; break;
                    }
                    else 
                        direction = (direction + 1) % 4;
                }
                if (direction == 2) {
                    if (col - 1 >= 0 && matrix[row][col - 1] != INT_MAX) {
                        --col; break;
                    }
                    else 
                        direction = (direction + 1) % 4;
                }
                if (direction == 3) {
                    if (row - 1 >= 0 && matrix[row - 1][col] != INT_MAX) {
                        --row; break;
                    }
                    else 
                        direction = (direction + 1) % 4;
                }
            }
        }

        return res;
    }
};

原始矩阵访问过的用INT_MAX标记，节省了空间。