# 1253. Reconstruct a 2-Row Binary Matrix
###### tags: `Leetcode` `Medium` `Greedy`
Link: https://leetcode.com/problems/reconstruct-a-2-row-binary-matrix/
## 思路
遍历colsum
如果colsum=2 说明upper和lower都要放
如果colsum=1 则需要考虑一下放哪边 因为后面出现2的时候 upper和lower都要放 消耗的数量一样 因此当下upper和lower哪个剩的多就把1放在哪边
如果把```lower<upper```改成```upper!=0```，就有可能出现最后遍历完upper=-2 lower=2的情况
## Code

class Solution {
    public List<List<Integer>> reconstructMatrix(int upper, int lower, int[] colsum) {
        int[][] res = new int[2][colsum.length];
        for(int i=0; i<colsum.length; i++){
            res[0][i] = colsum[i]==2 || (colsum[i]==1 && lower<upper)?1:0;
            res[1][i] = colsum[i]==2 || (colsum[i]==1 && res[0][i]!=1)?1:0;
            upper -= res[0][i];
            lower -= res[1][i];
        }
        return upper==0 && lower==0 ? new ArrayList(Arrays.asList(res[0], res[1])) : new ArrayList();
    }
}