# 1253. Reconstruct a 2-Row Binary Matrix

Given the following details of a matrix with `n` columns and `2` rows :

• The matrix is a binary matrix, which means each element in the matrix can be `0` or `1`.
• The sum of elements of the 0-th(upper) row is given as `upper`.
• The sum of elements of the 1-st(lower) row is given as `lower`.
• The sum of elements in the i-th column(0-indexed) is `colsum[i]`, where `colsum` is given as an integer array with length `n`.

Your task is to reconstruct the matrix with `upper``lower` and `colsum`.

Return it as a 2-D integer array.

If there are more than one valid solution, any of them will be accepted.

If no valid solution exists, return an empty 2-D array.

Example 1:

``````Input: upper = 2, lower = 1, colsum = [1,1,1]
Output: [[1,1,0],[0,0,1]]
Explanation: [[1,0,1],[0,1,0]], and [[0,1,1],[1,0,0]] are also correct answers.
``````

Example 2:

``````Input: upper = 2, lower = 3, colsum = [2,2,1,1]
Output: []
``````

Example 3:

``````Input: upper = 5, lower = 5, colsum = [2,1,2,0,1,0,1,2,0,1]
Output: [[1,1,1,0,1,0,0,1,0,0],[1,0,1,0,0,0,1,1,0,1]]
``````

Constraints:

• `1 <= colsum.length <= 10^5`
• `0 <= upper, lower <= colsum.length`
• `0 <= colsum[i] <= 2`

``````class Solution {
public:
vector<vector<int>> reconstructMatrix(int upper, int lower, vector<int>& colsum) {
vector<vector<int>> res(2, vector<int>(colsum.size()));
for (int i = 0; i < colsum.size(); ++i) {
res[0][i] = colsum[i] == 2 || (colsum[i] == 1 && upper > lower);
res[1][i] = colsum[i] == 2 || (colsum[i] == 1 && !res[0][i]);
upper -= res[0][i];
lower -= res[1][i];
}
return upper == 0 && lower == 0 ? res : vector<vector<int>>();
}
};
``````

Github 同步地址:

https://github.com/grandyang/leetcode/issues/1253

Find Valid Matrix Given Row and Column Sums

https://leetcode.com/problems/reconstruct-a-2-row-binary-matrix/

https://leetcode.com/problems/reconstruct-a-2-row-binary-matrix/discuss/425793/C%2B%2BJava-5-lines

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