Advanced Graph Algorithm

Minimum Spanning Tree

Properites:

# It’s a tree which means there’s no cycle # It’s based on non-directed graph

How to find a spanning tree?

Core idea is to use greedy algorithm and for each step find the edge with minimum weight.

Two ways to build:

# Kruskal’s algorithm:

Sort the edge based on weight, then adding each edge to the tree without forming a cycle.

# Prim’s algorithm

Starting from any vertex, insert the adjacent vertices into PQ, and choose the vertex with minimum edge weight

Data Structure:

Priority Queue Union Find

Dijkstra’s algorithm

Single Source Shortest Path Dijkstra’s algorithm initializing dist[s] to 0 and all other distTo[] entries to positive infinity. Then, it repeatedly relaxes and adds to the tree a non-tree vertex with the lowest distTo[] value, continuing until all vertices are on the tree or no non-tree vertex has a finite distTo[] value.

Data Structures:

. Priority Queue . Edges on the shortest-paths tree: edgeTo[v] is the the last edge on a shortest path from s to v. . Distance to the source: distTo[v] is the length of the shortest path from s to v.

Edge_weighted DAG

Negative Cycles:

Bellman-Ford algorithm.

Initialize distTo[s] to 0 and all other distTo[] values to infinity. Then, considering the digraph’s edges in any order, and relax all edges. Make V such passes:

for (int pass = 0; pass < G.V(); pass++)
   for (int v = 0; v < G.V(); v++)
      for (DirectedEdge e : G.adj(v))
          relax(e);

Arbitrage detection. Consider a market for financial transactions that is based on trading commodities.