README_EN.md

1253. Reconstruct a 2-Row Binary Matrix

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Description

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

Solutions

Python3

class Solution:
    def reconstructMatrix(self, upper: int, lower: int, colsum: List[int]) -> List[List[int]]:
        n = len(colsum)
        ans = [[0] * n for _ in range(2)]
        for j, v in enumerate(colsum):
            if v == 2:
                ans[0][j] = ans[1][j] = 1
                upper, lower = upper - 1, lower - 1
            if v == 1:
                if upper > lower:
                    upper -= 1
                    ans[0][j] = 1
                else:
                    lower -= 1
                    ans[1][j] = 1
            if upper < 0 or lower < 0:
                return []
        return ans if lower == upper == 0 else []

Java

class Solution {
    public List<List<Integer>> reconstructMatrix(int upper, int lower, int[] colsum) {
        int n = colsum.length;
        List<List<Integer>> ans = new ArrayList<>();
        List<Integer> first = new ArrayList<>();
        List<Integer> second = new ArrayList<>();
        for (int j = 0; j < n; ++j) {
            if (colsum[j] == 2) {
                first.add(1);
                second.add(1);
                upper--;
                lower--;
            } else if (colsum[j] == 1) {
                if (upper > lower) {
                    upper--;
                    first.add(1);
                    second.add(0);
                } else {
                    lower--;
                    first.add(0);
                    second.add(1);
                }
            } else {
                first.add(0);
                second.add(0);
            }
            if (upper < 0 || lower < 0) {
                return ans;
            }
        }
        if (upper != 0 || lower != 0) {
            return ans;
        }
        ans.add(first);
        ans.add(second);
        return ans;
    }
}

C++

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

Go

func reconstructMatrix(upper int, lower int, colsum []int) [][]int {
	n := len(colsum)
	ans := make([][]int, 2)
	for i := range ans {
		ans[i] = make([]int, n)
	}
	for j, v := range colsum {
		if v == 2 {
			ans[0][j], ans[1][j] = 1, 1
			upper--
			lower--
		}
		if v == 1 {
			if upper > lower {
				upper--
				ans[0][j] = 1
			} else {
				lower--
				ans[1][j] = 1
			}
		}
		if upper < 0 || lower < 0 {
			return [][]int{}
		}
	}
	if upper != 0 || lower != 0 {
		return [][]int{}
	}
	return ans
}

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