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# Program to find path with maximum probability using Python

Suppose we have an undirected weighted graph with n nodes (nodes are numbered from 0 onwards), This graph is given as input using edge list, for each edge e, it has a probability of success of traversing that edge probability[e]. We also have start and end nodes, we have to find the path with the maximum probability of success to go from start to end and return its success probability. If we cannot find any path, then return 0.

So, if the input is like

then the output will be 0.24 because there are two paths from node 0 to 2, one with probability 0.2, another one via node 1 has probability 0.4*0.6 = 0.24, this is maximum.

To solve this, we will follow these steps −

g := make graph from given edge list and use probability value as weight

q := a queue data structure

insert (start, 1) into q

visited := a map to hold visited node

while q is not empty, do

(node, prob) := first item of q and delete it from q

if visited[node] > prob, then

go for next iteration

otherwise,

visited[node] := prob

for each adjacent node adj and probability nextProb in g[node], do

if visited[adj] < prob * nextProb, then

insert (adj, prob * nextProb) at the end of q

return visited[end]

Let us see the following implementation to get better understanding −

## Example

from collections import defaultdict, deque def solve(edges, probability, start, end): g = defaultdict(list) for i in range(len(edges)): src, dst = edges[i][0], edges[i][1] prob = probability[i] g[src].append((dst, prob)) g[dst].append((src, prob)) q = deque() q.append((start, 1)) visited = defaultdict(int) while q: node, prob = q.popleft() if visited[node] > prob: continue else: visited[node] = prob for adj, nextProb in g[node]: if visited[adj] < prob * nextProb: q.append((adj, prob * nextProb)) return visited[end] edges = [[0,1],[1,2],[0,2]] probability = [0.5,0.5,0.2] start = 0 end = 2 print(solve(edges, probability, start, end))

## Input

[[0,1],[1,2],[0,2]], [0.5,0.5,0.2], 0, 2

## Output

0.25

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