Check if alternate path exists from U to V with smaller individual weight in a given Graph
Given a directed weighted graph with N vertices and M edges and an edge (U, V). The task is to find whether there is an alternate path present from U to V with individual weight of edges in alternate path less than the weight of direct path. If present print Yes else print No.
Examples
For the given directed graph:
Input: N = 7, M = 10, U = 3, V = 6.
Output: No
Explanation:
For the given edge {3, 6}, weight = 16. There is no alternate path to reach 6 from 3. Hence the answer is No.
Input: N = 7, M = 10, U = 1, V = 6.
Output: Yes
Explanation:
=> For the given edge {1, 6}, weight = 5.
=> Alternate path to reach 6 from 1 = {1, 5, 6} with individual weights {12, 2} which is more than 5. Hence this path cannot be considered.
=> Alternate path to reach 6 from 1 = {1, 2, 4, 5, 6} with individual weights {5, 1, 1, 2} which is not less than 5. Hence this path cannot be considered.
=> Alternate path to reach 6 from 1 = {1, 4, 5, 6} with individual weights {3, 1, 2} which is less than 5. Hence this path can be considered.
=> Hence the answer is Yes
Approach:
- Traverse the given Directed Graph with starting vertex U using depth-first search (DFS) Traversal.
- During DFS Traversal if weight of any edge is greater than the directed edge, then that path is not included.
- If we reach the vertex V with weight of each edge in traverse path less than directed edge, then there exists an alternate path.
- Else there is no path between vertex U and vertex V other than direct path.
Below is the implementation of the above approach:
C++14
// C++ program for above approach #include <bits/stdc++.h> using namespace std; // Edge class class Edge { public: int u; int v; int w; // Edge constructor to // initialize edge (u, v) with // weight w Edge(int u, int v, int w) { this->u = u; this->v = v; this->w = w; } }; class GFG{ public: // Array to mark already // visited vertices bool *visited; // Adjacency list representation // of the graph vector<Edge *> *graph; // GfG class constructor GFG(int size) { visited = new bool[size]; graph = new vector<Edge *>[size]; } // Depth First Search to traverse // all vertices with weight less // than weight of the dfs root void dfs(int S, int W) { // Marking the vertex visited visited[S] = true; // Traversing adjacent vertex for(Edge *uv : graph[S]) { int ver = uv->v; int w = uv->w; if (!visited[ver] && w < W) dfs(ver, W); } } }; // Driver code int main() { // Number of vertices int N = 7; // Number of edges int M = 10; // Edge to be checked int U_V[] = {3, 6}; // Creating GfG object GFG *obj = new GFG(8); // Creating edges Edge *e0 = new Edge(1, 2, 5); Edge *e1 = new Edge(1, 4, 3); Edge *e2 = new Edge(1, 5, 12); Edge *e3 = new Edge(1, 6, 5); Edge *e4 = new Edge(4, 5, 1); Edge *e5 = new Edge(5, 6, 2); Edge *e6 = new Edge(5, 3, 1); Edge *e7 = new Edge(3, 6, 16); Edge *e8 = new Edge(4, 7, 1); Edge *e9 = new Edge(2, 4, 1); // Adding edges to the graph obj->graph[1].push_back(e0); obj->graph[1].push_back(e1); obj->graph[1].push_back(e2); obj->graph[1].push_back(e3); obj->graph[4].push_back(e4); obj->graph[5].push_back(e5); obj->graph[5].push_back(e6); obj->graph[3].push_back(e7); obj->graph[4].push_back(e8); obj->graph[2].push_back(e9); // DFS traversal from // vertex U obj->dfs(U_V[0], 16); // If there is alternate // path then print YES, // else NO if (obj->visited[U_V[1]]) { cout << "NO" << endl; } else { cout << "YES" << endl; } } // This code is contributed by sanjeev2552 |
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Java
// Java program for above approach import java.util.*; // To ignore the unchecked warning @SuppressWarnings("unchecked") // GfG class public class GfG { // Array to mark already // visited vertices static private boolean visited[]; // Adjacency list representation // of the graph static private ArrayList<Edge> graph[]; // GfG class constructor public GfG(int size) { visited = new boolean[size]; graph = new ArrayList[size]; } // Edge class static class Edge { int u; int v; int w; // Edge constructor to // initialize edge (u, v) with // weight w Edge(int u, int v, int w) { this.u = u; this.v = v; this.w = w; } } // Helper method to // initialize graph static private void helperInitialize(int size) { for (int i = 0; i < size; i++) { graph[i] = new ArrayList<Edge>(); } } // Depth First Search to traverse // all vertices with weight less // than weight of the dfs root static private void dfs(int S, int W) { // Marking the vertex visited visited[S] = true; // Traversing adjacent vertex for (Edge uv : graph[S]) { int ver = uv.v; int w = uv.w; if (!visited[ver] && w < W) dfs(ver, W); } } // Driver function public static void main(String[] args) { // Number of vertices int N = 7; // Number of edges int M = 10; // Edge to be checked int U_V[] = { 3, 6 }; // Creating GfG object GfG obj = new GfG(8); // Initializing graph helperInitialize(8); // Creating edges Edge e0 = new Edge(1, 2, 5); Edge e1 = new Edge(1, 4, 3); Edge e2 = new Edge(1, 5, 12); Edge e3 = new Edge(1, 6, 5); Edge e4 = new Edge(4, 5, 1); Edge e5 = new Edge(5, 6, 2); Edge e6 = new Edge(5, 3, 1); Edge e7 = new Edge(3, 6, 16); Edge e8 = new Edge(4, 7, 1); Edge e9 = new Edge(2, 4, 1); // Adding edges to the graph graph[1].add(e0); graph[1].add(e1); graph[1].add(e2); graph[1].add(e3); graph[4].add(e4); graph[5].add(e5); graph[5].add(e6); graph[3].add(e7); graph[4].add(e8); graph[2].add(e9); // DFS traversal from // vertex U dfs(U_V[0], 16); // If there is alternate // path then print YES, // else NO if (visited[U_V[1]]) { System.out.print("No"); } else { System.out.print("Yes"); } } } |
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Python3
# Python3 program for above approach class Edge: # Edge constructor to # initialize edge (u, v) with # weight w def __init__(self, u, v, w): self.u = u self.v = v self.w = w # Depth First Search to traverse # all vertices with weight less # than weight of the dfs root def dfs(S, W): global visited,graph # Marking the vertex visited visited[S] = True # Traversing adjacent vertex for uv in graph[S]: ver = uv.v w = uv.w if (not visited[ver] and w < W): dfs(ver, W) # Driver code if __name__ == '__main__': # Number of vertices N = 7 # Number of edges M = 10 # Edge to be checked U_V = [3, 6] # Creating GfG object visited, graph = [False for i in range(8)], [[] for i in range(8)] # Creating edges e0 = Edge(1, 2, 5) e1 = Edge(1, 4, 3) e2 = Edge(1, 5, 12) e3 = Edge(1, 6, 5) e4 = Edge(4, 5, 1) e5 = Edge(5, 6, 2) e6 = Edge(5, 3, 1) e7 = Edge(3, 6, 16) e8 = Edge(4, 7, 1) e9 = Edge(2, 4, 1) # Adding edges to the graph graph[1].append(e0) graph[1].append(e1) graph[1].append(e2) graph[1].append(e3) graph[4].append(e4) graph[5].append(e5) graph[5].append(e6) graph[3].append(e7) graph[4].append(e8) graph[2].append(e9) # DFS traversal from # vertex U dfs(U_V[0], 16) # If there is alternate # path then prYES, # else NO if (visited[U_V[1]]): print("NO") else : print("YES") # This code is contributed by mohit kumar 29 |
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C#
// C# program for above approach using System; using System.Collections.Generic; // GfG class class GfG { // Array to mark already // visited vertices static private bool []visited; // Adjacency list representation // of the graph static private List<Edge> []graph; // GfG class constructor public GfG(int size) { visited = new bool[size]; graph = new List<Edge>[size]; } // Edge class class Edge { public int u; public int v; public int w; // Edge constructor to // initialize edge (u, v) with // weight w public Edge(int u, int v, int w) { this.u = u; this.v = v; this.w = w; } } // Helper method to // initialize graph static private void helperInitialize(int size) { for (int i = 0; i < size; i++) { graph[i] = new List<Edge>(); } } // Depth First Search to traverse // all vertices with weight less // than weight of the dfs root static private void dfs(int S, int W) { // Marking the vertex visited visited[S] = true; // Traversing adjacent vertex foreach (Edge uv in graph[S]) { int ver = uv.v; int w = uv.w; if (!visited[ver] && w < W) dfs(ver, W); } } // Driver function public static void Main(String[] args) { // Edge to be checked int []U_V = { 3, 6 }; // Creating GfG object GfG obj = new GfG(8); // Initializing graph helperInitialize(8); // Creating edges Edge e0 = new Edge(1, 2, 5); Edge e1 = new Edge(1, 4, 3); Edge e2 = new Edge(1, 5, 12); Edge e3 = new Edge(1, 6, 5); Edge e4 = new Edge(4, 5, 1); Edge e5 = new Edge(5, 6, 2); Edge e6 = new Edge(5, 3, 1); Edge e7 = new Edge(3, 6, 16); Edge e8 = new Edge(4, 7, 1); Edge e9 = new Edge(2, 4, 1); // Adding edges to the graph graph[1].Add(e0); graph[1].Add(e1); graph[1].Add(e2); graph[1].Add(e3); graph[4].Add(e4); graph[5].Add(e5); graph[5].Add(e6); graph[3].Add(e7); graph[4].Add(e8); graph[2].Add(e9); // DFS traversal from // vertex U dfs(U_V[0], 16); // If there is alternate // path then print YES, // else NO if (visited[U_V[1]]) { Console.Write("No"); } else { Console.Write("Yes"); } } } // This code is contributed by 29AjayKumar |
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Output:
Yes
Time Complexity: O(N + M), where N = number of vertices & M = munber of edges.
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