演化樹是分析生物演化關係的重要資料結構。然而，根據不同資訊或是方法建構的演化樹可能會有不同的結構。目前有數種方法解決此種衝突，其中最常被使用的一種為一致樹。此方法建構出數個演化樹的一致樹以統整其共有的資訊。 Adams 於 1972 年提出第一個一致樹的方法，稱為 Adams 一致樹。此後，有多種一致樹被提出且深入研究。其中有些也被實作於常用的生物資訊軟體中。
本論首先分析各種一致樹，介紹其定義並且統整其已知演算法之時間。此外，本論文亦提出一個時間複雜度 O(k^2n)
的演算法，其中 n 為物種數而 k 為輸入之演化樹個數。在此之前本問題的最佳演算法為 Jansson et al.
提出，時間複雜度為 min{O(kn^2), O(kn(k + log^2 n))}。Jansson et al. 亦建議改進其 O(kn(k + log^2 n)
時間之演算法以到 O(k^2n) 之時間，本論文所提出之演算法有效達成此一目標。

Phylogenies are important structures for analyzing the evolutionary rela-tionships among species. However, phylogenies obtained from different data sets or methods may lead to different structures. Several methods have been proposed to resolve such conflicts. One of the most popular approaches is the consensus tree method, which constructs a consensus tree to summarize the in-formation common to a collection of different phylogenies on the same set of species. Adams introduced the first method called Adams consensus tree in 1972. Since then, numerous consensus tree methods have been proposed and extensively studied. Some of them are also implemented in popular computational phylogenetic software packages.
In this thesis, a comprehensive review on consensus tree methods is first presented. For each method, its definition is introduced and its known complexity results are summarized. Additionally, this thesis also provides an efficient O(k^2n)-time algorithm for the frequency difference consensus tree problem, which is one of the more recent consensus tree methods. The previous best upper bound of this problem is min{O(kn^2), O(kn(k + log^2n))} by Jansson et al., where n is the number of species and k is the number of input trees. Jansson et al. suggested further improving their O(kn(k + log^2n)) upper bound to O(k^2n) as an open problem. The algorithm presented in this thesis gives a positive answer to their question.

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