LeetCode 1253. Reconstruct a 2-Row Binary Matrix

1, the original title 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

2, a brief translation:

Construction of a plurality of data rows two columns, and the first row of upper, and the second row of Lower, and to colsum [i] of the i-th column. If such an array does not exist returns NULL

 

3, code analysis:

• If the upper + lower does not mean colsum and then return empty.
• If the number 2 is greater than colsum in upper or lower, return null
• From left to right, a premise is inserted vertically keep balance. (When colums [i] == 1, if lower> = upper plug, the plug remaining cases)

4, answer the code:

public List<List<Integer>> reconstructMatrix(int upper, int lower, int[] colums) {
        int sum = 0;
        int numof2 = 0;
        for (int colum : colums) {
            sum += colum;
            if (colum == 2) {
                numof2++;
            }
        }
        List<List<Integer>> result = new ArrayList<>();
        if (sum != upper + lower || numof2 > Math.min(upper, lower)) {
            return result;
        }
        List<Integer> upperList = new ArrayList<>();
        List<Integer> lowerList = new ArrayList<>();
        result.add(upperList);
        result.add(lowerList);
        for (int colum : colums) {
            if (colum == 0) {
                upperList.add(0);
                lowerList.add(0);
            } else if (colum == 2) {
                upperList.add(1);
                upper--;
                lowerList.add(1);
                lower--;
            } else {
                if (upper > lower) {
                    upperList.add(1);
                    lowerList.add(0);
                    upper--;
                } else {
                    upperList.add(0);
                    lowerList.add(1);
                    lower--;
                }
            }
        }
        return result;
    }