39. Consider the following 10 problems and algorithms. (1) Merge sort for sorting problem (2) Heap sort for sorting problem. (3) Minimum spanning tree problem. (4) Floyd-Marshall algorithm for all pairs shortest path problem. (5) Finding a maximum independent set in a time interval graph. (6) Huffman's algorithm for Huffman code problem. (7) Strassen's matrix multiplication algorithm. (8) Constructing an optimal binary search tree for weighted searching problem, i.e to minimize the expected searching time. (9) Longest Common subsequence problem. (10) The Ford-Fulkerson method for maximum flow problem.

Each of the above problems (or algorithms) can be solved by (or classified as) one of the following design techniques

1. Divide and Conquer, 2. Dynamic Programming, 3. Greedy method, 4. Others (none of the above three techniques).

Among the above 10 problems, there are x, y, z, w of them respectively that can be solved by(or classified as) design technique 1, 2, 3, 4 respectively. Find x, y, z, and w, then choose the following correct ones.