498-对角线遍历

LeetCode 498. Diagonal Traverse

LeetCode-498

Given an m x n matrix mat, return an array of all the elements of the array in a diagonal order.

Example 1:

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

Example 2:

Input: mat = [[1,2],[3,4]]
Output: [1,2,3,4]

method

储备知识：mat[i][j]对应的对角线就是i+j

• i+j是偶数：左下->右上，下标变化是i--,j++
• i+j是奇数：右上->左下，下标变化是i++,j--

vector<int> findDiagonalOrder(vector<vector<int>>& mat) {
    int n = mat.size(), m = mat[0].size();
    vector<int> res;
    for (int i = 0; i < n + m - 1; i++) {
        int x = 0, y = 0;
        if (i % 2 == 0) {
            x = i < n ? i : n - 1;  // 是否超过行数
            y = i - x;
            while (x >= 0 && y < m) {
                res.push_back(mat[x][y]);
                x--, y++;
            }
        }
        else {
            y = i < m ? i : m - 1;  // 是否超过列数
            x = i - y;
            while (x < n && y >= 0) {
                res.push_back(mat[x][y]);
                x++, y--;
            }
        }
    }
    return res;
}