compressed vector multiplication

第二题  给两个数组，两个数组中的元素都是pair<int, int>，数组表示压缩后的一串数字

A: [(1, 2), (3,1), (2,3), (3, 1)] 表示 {1, 1, 3, 2, 2, 2, 3}

B: [(5, 1), (1,1), (3,4), (2, 1)] 表示 {5, 1, 3, 3, 3, 3, 2}

求A点乘B的结果，以压缩形式的返回。以上面的A，B为例，结果是[(5,1), (1,1), (9,1), (6,4)]

要求不能展开A和B以后做乘法再压缩。

 

class Solution {
    public static void main(String[] args) {
        // A: [(1, 2), (3,1), (2,3), (3, 1)] 表示 {1, 1, 3, 2, 2, 2, 3}
        // B: [(5, 1), (1,1), (3,4), (2, 1)] 表示 {5, 1, 3, 3, 3, 3, 2}
        // 求A点乘B的结果，以压缩形式的返回。以上面的A，B为例，结果是[(5,1), (1,1), (9,1), (6,4)]

        Pair pair1 = new Pair(1, 2);
        Pair pair2 = new Pair(3, 1);
        Pair pair3 = new Pair(2, 3);
        Pair pair4 = new Pair(3, 1);
        Pair pair5 = new Pair(5, 1);
        Pair pair6 = new Pair(1, 1);
        Pair pair7 = new Pair(3, 4);
        Pair pair8 = new Pair(2, 1);

        List<Pair> list1 = Arrays.asList(pair1, pair2, pair3, pair4);
        List<Pair> list2 = Arrays.asList(pair5, pair6, pair7, pair8);

        Solution s = new Solution();
        List<Pair> result = s.compressedVectorMultiplication(list1, list2);
        System.out.println(result);
    }

    public List<Pair> compressedVectorMultiplication(List<Pair> list1, List<Pair> list2) {
        List<Pair> result = new ArrayList<>();
        int idx1 = 0, idx2 = 0;

        while (idx1 < list1.size() && idx2 < list2.size()) {
            Pair p1 = list1.get(idx1);
            Pair p2 = list2.get(idx2);

            int value = p1.val * p2.val;
            int count = Math.min(p1.count, p2.count);

            if (result.isEmpty() || result.get(result.size() - 1).val != value) {
                result.add(new Pair(value, count));
            } else {
                result.get(result.size() - 1).count += count;
            }

            p1.count -= count;
            p2.count -= count;

            if (p1.count == 0) {
                idx1++;
            }

            if (p2.count == 0) {
                idx2++;
            }
        }
        return result;
    }
}

class Pair {
    int val;
    int count;

    public Pair(int val, int count) {
        this.val = val;
        this.count = count;
    }

    public String toString() {
        return "(" + val + "," + count + ")";
    }
}