054.md

54. Spiral Matrix

Solution 1 (O(mn))

class Solution {
public:
    vector<int> spiralOrder(vector<vector<int>>& matrix) {
        vector<int> ans;
        int m = matrix.size();
        if (m == 0) return ans;
        int n = matrix[0].size();
        if (n == 0) return ans;
        int top = 0, bottom = m - 1, left = 0, right = n - 1;
        while (top < bottom && left < right) {
            for (int i = left; i < right; i++)
                ans.push_back(matrix[top][i]);
            for (int i = top; i < bottom; i++)
                ans.push_back(matrix[i][right]);
            for (int i = right; i > left; i--)
                ans.push_back(matrix[bottom][i]);
            for (int i = bottom; i > top; i--)
                ans.push_back(matrix[i][left]);
            top++;
            bottom--;
            left++;
            right--;
        }
        if (top == bottom && left == right) {
            ans.push_back(matrix[top][left]);
        } else if (top == bottom) {
            for (int i = left; i <= right; i++) {
                ans.push_back(matrix[top][i]);
            }
        } else if (left == right) {
            for (int i = top; i <= bottom; i++) {
                ans.push_back(matrix[i][left]);
            }
        }
        return ans;
    }
};