498. Diagonal Traverse

Problem:

Given a matrix of M x N elements (M rows, N columns), return all elements of the matrix in diagonal order as shown in the below image.

Example:

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

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

Explanation:

Note:

The total number of elements of the given matrix will not exceed 10,000.

思路：

Solution (C++):

vector<int> findDiagonalOrder(vector<vector<int>>& matrix) {
    if (matrix.empty())  return {};
    int m = matrix.size(), n = matrix[0].size();
    vector<vector<int>> tmp(m+n-1);
    
    for (int i = 0; i < m+n-1; ++i) {
        int row = max(0, i-n+1);
        int col = min(i, n-1);
        for (; row < m && col >= 0 ; ++row, --col) {
            tmp[i].push_back(matrix[row][col]);
        }
    }
    
    vector<int> res;
    for (int i = 0; i < m+n-1; ++i) {
        if (i & 1)  res.insert(res.end(), tmp[i].begin(), tmp[i].end());
        else  res.insert(res.end(), tmp[i].rbegin(), tmp[i].rend());
    }
    return res;
}

性能：

Runtime: 116 ms  Memory Usage: 16.9 MB

思路：

Solution (C++):

性能：

Runtime: ms  Memory Usage: MB