Arbitrages: First working version

Arbitrages/cs412_arbitrages_a.py

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+"""
+name: Nicholas Tamassia
+
+Honor Code and Acknowledgments:
+
+        This work complies with the JMU Honor Code.
+
+       Comments here on your code and submission.
+"""
+
+import math
+from collections import defaultdict
+
+
+def find_arbitrage(graph: dict[str, dict[str, float]]) -> list[str] | None:
+    weights: dict[str, float] = {c: math.inf for c in graph}
+    prev: dict[str, str | None] = {c: None for c in graph}
+    start: str = list(graph.keys())[0]
+
+    weights[start] = 0
+    for _ in range(len(graph) - 1):
+        for src in graph:
+            for dest, rate in graph[src].items():
+                weight: float = -math.log(rate)
+                if weights[src] + weight < weights[dest]:
+                    weights[dest] = weights[src] + weight
+                    prev[dest] = src
+
+    node: str | None = None
+    for src in graph:
+        for dest, rate in graph[src].items():
+            weight: float = -math.log(rate)
+            if weights[src] + weight < weights[dest]:
+                node = dest
+                prev[dest] = src
+                break
+        if node is not None:
+            break
+
+    if node is None:
+        return
+
+    for _ in range(len(graph)):
+        node = prev[node]
+
+    path = [node]
+    while True:
+        node = prev[node]
+        path.append(node)
+        if node == path[0]:
+            break
+
+    path.reverse()
+
+    return path
+
+
+def main():
+    n: int = int(input().strip())
+    graph: dict[str, dict[str, float]] = defaultdict(dict)
+
+    for _ in range(n):
+        vals: list[str] = input().strip().split()
+        src: str = vals[0]
+        dest: str = vals[1]
+        rate: float = float(vals[2])
+        graph[src][dest] = rate
+
+    path = find_arbitrage(graph)
+    if path is not None:
+        print("Arbitrage Detected")
+        print(" => ".join(path))
+
+        factor = 1.0
+        for i in range(len(path) - 1):
+            factor *= graph[path[i]][path[i + 1]]
+        print(f"{factor:.5f} factor increase")
+    else:
+        print("No Arbitrage Detected")
+
+
+if __name__ == "__main__":
+    main()