尝试用贪心算法和动态规划算法构造最优二叉搜索树，并做基本统计分析和比较。结论是贪心算法不能保证构造出最优，也没有好的效率；动态规划明显更好。-Use greedy algorithm and dynamic programming to build optimal binary search tree. And related statistics and comparison are provided in report.