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The idea is just to add the elements in the spiral order. First the up-most row (u), then the right-most column (r), then the down-most row (d), and finally the left-most column (l). After finishing a row or a column, update the corresponding variable to continue the process.
The code is as follows.
1 class Solution { 2 public: 3 vector<int> spiralOrder(vector<vector<int>>& matrix) { 4 if (matrix.empty()) return {}; 5 int m = matrix.size(), n = matrix[0].size(); 6 vector<int> spiral(m * n); 7 int u = 0, d = m - 1, l = 0, r = n - 1, k = 0; 8 while (true) { 9 // up 10 for (int col = l; col <= r; col++) spiral[k++] = matrix[u][col]; 11 if (++u > d) break; 12 // right 13 for (int row = u; row <= d; row++) spiral[k++] = matrix[row][r]; 14 if (--r < l) break; 15 // down 16 for (int col = r; col >= l; col--) spiral[k++] = matrix[d][col]; 17 if (--d < u) break; 18 // left 19 for (int row = d; row >= u; row--) spiral[k++] = matrix[row][l]; 20 if (++l > r) break; 21 } 22 return spiral; 23 } 24 };
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原文地址：http://www.cnblogs.com/jcliBlogger/p/4719962.html
