Given a binary tree having N nodes and weight of N-1 edges. The distance between two nodes is the sum of the weight of edges on the path between two nodes. Each query contains two integers U and V, the task is to find the distance between nodes U and V.
Examples:
Input:
Output: 3 5 12 12
Explanation:
Distance between nodes 1 to 3 = weight(1, 3) = 2
Distance between nodes 2 to 3 = weight(1, 2) + weight(1, 3) = 5
Distance between nodes 3 to 5 = weight(1, 3) + weight(1, 2) + weight(2, 5) = 12
Distance between nodes 4 to 5 = weight(4, 2) + weight(2, 5) = 12
Approach: The idea is to use LCA in a tree using Binary Lifting Technique.
- Binary Lifting is a Dynamic Programming approach where we pre-compute an array lca[i][j] where i = [1, n], j = [1, log(n)] and lca[i][j] contains 2j-th ancestor of node i.
- For computing the values of lca[][], the following recursion may be used
![lca[i][j] =\begin{cases} parent[i] & \text{ ;if } j=0 \\ lca[lca[i][j - 1]][j - 1] & \text{ ;if } j>0 \end{cases}](https://geeksforgeeks.org/wp-content/uploads/2023/10/dominic_rubhabha_quicklatex.com-9f156ce8720a0936dd8daded78c997a2_l3.png "Rendered by QuickLaTeX.com")
- As we will compute the lca[][] array we will also calculate the distance[][] where distance[i][j] contains the distance from node i to its 2j-th ancestor
- For computing the values of dist[][], the following recursion may be used.
![dist[i][j] =\begin{cases} cost(i, parent[i]) & \text{ ;if } j=0 \\ dist[i][j] = dist[i][j - 1] + dist[lca[i][j - 1]][j - 1]; & \text{ ;if } j>0 \end{cases}](https://geeksforgeeks.org/wp-content/uploads/2023/10/rubhabha_quicklatex.com-27ab8eb4ac9136709d373b60bb98409e_l3.png "Rendered by QuickLaTeX.com")
- After precomputation, we find the distance between (u, v) as we find the least common ancestor of (u, v).
Below is the implementation of the above approach:
C++
// C++ Program to find distance// between two nodes using LCA#include <bits/stdc++.h>using namespace std;#define MAX 1000#define log 10 // log2(MAX)// Array to store the level// of each nodeint level[MAX];int lca[MAX][log];int dist[MAX][log];// Vector to store treevector<pair<int, int> > graph[MAX];void addEdge(int u, int v, int cost){ graph[u].push_back({ v, cost }); graph[v].push_back({ u, cost });}// Pre-Processing to calculate// values of lca[][], dist[][]void dfs(int node, int parent, int h, int cost){ // Using recursion formula to // calculate the values // of lca[][] lca[node][0] = parent; // Storing the level of // each node level[node] = h; if (parent != -1) { dist[node][0] = cost; } for (int i = 1; i < log; i++) { if (lca[node][i - 1] != -1) { // Using recursion formula to // calculate the values of // lca[][] and dist[][] lca[node][i] = lca[lca[node] [i - 1]] [i - 1]; dist[node][i] = dist[node][i - 1] + dist[lca[node][i - 1]] [i - 1]; } } for (auto i : graph[node]) { if (i.first == parent) continue; dfs(i.first, node, h + 1, i.second); }}// Function to find the distance// between given nodes u and vvoid findDistance(int u, int v){ int ans = 0; // The node which is present // farthest from the root node // is taken as v. If u is // farther from root node // then swap the two if (level[u] > level[v]) swap(u, v); // Finding the ancestor of v // which is at same level as u for (int i = log - 1; i >= 0; i--) { if (lca[v][i] != -1 && level[lca[v][i]] >= level[u]) { // Adding distance of node // v till its 2^i-th ancestor ans += dist[v][i]; v = lca[v][i]; } } // If u is the ancestor of v // then u is the LCA of u and v if (v == u) { cout << ans << endl; } else { // Finding the node closest to the // root which is not the common // ancestor of u and v i.e. a node // x such that x is not the common // ancestor of u and v but lca[x][0] is for (int i = log - 1; i >= 0; i--) { if (lca[v][i] != lca[u][i]) { // Adding the distance // of v and u to // its 2^i-th ancestor ans += dist[u][i] + dist[v][i]; v = lca[v][i]; u = lca[u][i]; } } // Adding the distance of u and v // to its first ancestor ans += dist[u][0] + dist[v][0]; cout << ans << endl; }}// Driver Codeint main(){ // Number of nodes int n = 5; // Add edges with their cost addEdge(1, 2, 2); addEdge(1, 3, 3); addEdge(2, 4, 5); addEdge(2, 5, 7); // Initialising lca and dist values // with -1 and 0 respectively for (int i = 1; i <= n; i++) { for (int j = 0; j < log; j++) { lca[i][j] = -1; dist[i][j] = 0; } } // Perform DFS dfs(1, -1, 0, 0); // Query 1: {1, 3} findDistance(1, 3); // Query 2: {2, 3} findDistance(2, 3); // Query 3: {3, 5} findDistance(3, 5); return 0;} |
Java
// Java program to find distance// between two nodes using LCAimport java.io.*;import java.util.*;class GFG{static final int MAX = 1000;// log2(MAX)static final int log = 10;// Array to store the level// of each nodestatic int[] level = new int[MAX];static int[][] lca = new int[MAX][log];static int[][] dist = new int[MAX][log];// Vector to store tree@SuppressWarnings("unchecked")static List<List<int[]> > graph = new ArrayList();static void addEdge(int u, int v, int cost){ graph.get(u).add(new int[]{ v, cost }); graph.get(v).add(new int[]{ u, cost });}// Pre-Processing to calculate// values of lca[][], dist[][]static void dfs(int node, int parent, int h, int cost){ // Using recursion formula to // calculate the values // of lca[][] lca[node][0] = parent; // Storing the level of // each node level[node] = h; if (parent != -1) { dist[node][0] = cost; } for(int i = 1; i < log; i++) { if (lca[node][i - 1] != -1) { // Using recursion formula to // calculate the values of // lca[][] and dist[][] lca[node][i] = lca[lca[node][i - 1]][i - 1]; dist[node][i] = dist[node][i - 1] + dist[lca[node][i - 1]][i - 1]; } } for(int[] i : graph.get(node)) { if (i[0] == parent) continue; dfs(i[0], node, h + 1, i[1]); }}// Function to find the distance// between given nodes u and vstatic void findDistance(int u, int v){ int ans = 0; // The node which is present // farthest from the root node // is taken as v. If u is // farther from root node // then swap the two if (level[u] > level[v]) { int temp = u; u = v; v = temp; } // Finding the ancestor of v // which is at same level as u for(int i = log - 1; i >= 0; i--) { if (lca[v][i] != -1 && level[lca[v][i]] >= level[u]) { // Adding distance of node // v till its 2^i-th ancestor ans += dist[v][i]; v = lca[v][i]; } } // If u is the ancestor of v // then u is the LCA of u and v if (v == u) { System.out.println(ans); } else { // Finding the node closest to the // root which is not the common // ancestor of u and v i.e. a node // x such that x is not the common // ancestor of u and v but lca[x][0] is for(int i = log - 1; i >= 0; i--) { if (lca[v][i] != lca[u][i]) { // Adding the distance // of v and u to // its 2^i-th ancestor ans += dist[u][i] + dist[v][i]; v = lca[v][i]; u = lca[u][i]; } } // Adding the distance of u and v // to its first ancestor ans += dist[u][0] + dist[v][0]; System.out.println(ans); }}// Driver Codepublic static void main(String[] args){ // Number of nodes int n = 5; for(int i = 0; i < MAX; i++) { graph.add(new ArrayList<int[]>()); } // Add edges with their cost addEdge(1, 2, 2); addEdge(1, 3, 3); addEdge(2, 4, 5); addEdge(2, 5, 7); // Initialising lca and dist values // with -1 and 0 respectively for(int i = 1; i <= n; i++) { for(int j = 0; j < log; j++) { lca[i][j] = -1; dist[i][j] = 0; } } // Perform DFS dfs(1, -1, 0, 0); // Query 1: {1, 3} findDistance(1, 3); // Query 2: {2, 3} findDistance(2, 3); // Query 3: {3, 5} findDistance(3, 5);}}// This code is contributed by jithin |
Python3
# Python3 Program to find # distance between two nodes # using LCAMAX = 1000# lg2(MAX)lg = 10# Array to store the level# of each nodelevel = [0 for i in range(MAX)]lca = [[0 for i in range(lg)] for j in range(MAX)]dist = [[0 for i in range(lg)] for j in range(MAX)]# Vector to store treegraph = [[] for i in range(MAX)]def addEdge(u, v, cost): global graph graph[u].append([v, cost]) graph[v].append([u, cost])# Pre-Processing to calculate# values of lca[][], dist[][]def dfs(node, parent, h, cost): # Using recursion formula to # calculate the values # of lca[][] lca[node][0] = parent # Storing the level of # each node level[node] = h if (parent != -1): dist[node][0] = cost for i in range(1, lg): if (lca[node][i - 1] != -1): # Using recursion formula to # calculate the values of # lca[][] and dist[][] lca[node][i] = lca[lca[node][i - 1]][i - 1] dist[node][i] = (dist[node][i - 1] + dist[lca[node][i - 1]][i - 1]) for i in graph[node]: if (i[0] == parent): continue dfs(i[0], node, h + 1, i[1])# Function to find the distance# between given nodes u and vdef findDistance(u, v): ans = 0 # The node which is present # farthest from the root node # is taken as v. If u is # farther from root node # then swap the two if (level[u] > level[v]): temp = u u = v v = temp # Finding the ancestor of v # which is at same level as u i = lg - 1 while(i >= 0): if (lca[v][i] != -1 and level[lca[v][i]] >= level[u]): # Adding distance of node # v till its 2^i-th ancestor ans += dist[v][i] v = lca[v][i] i -= 1 # If u is the ancestor of v # then u is the LCA of u and v if (v == u): print(ans) else: # Finding the node closest to the # root which is not the common # ancestor of u and v i.e. a node # x such that x is not the common # ancestor of u and v but lca[x][0] is i = lg - 1 while(i >= 0): if (lca[v][i] != lca[u][i]): # Adding the distance # of v and u to # its 2^i-th ancestor ans += dist[u][i] + dist[v][i] v = lca[v][i] u = lca[u][i] i -= 1 # Adding the distance of u and v # to its first ancestor ans += (dist[u][0] + dist[v][0]) print(ans)# Driver Codeif __name__ == '__main__': # Number of nodes n = 5 # Add edges with their cost addEdge(1, 2, 2) addEdge(1, 3, 3) addEdge(2, 4, 5) addEdge(2, 5, 7) # Initialising lca and dist values # with -1 and 0 respectively for i in range(1, n + 1): for j in range(lg): lca[i][j] = -1 dist[i][j] = 0 # Perform DFS dfs(1, -1, 0, 0) # Query 1: {1, 3} findDistance(1, 3) # Query 2: {2, 3} findDistance(2, 3) # Query 3: {3, 5} findDistance(3, 5) # This code is contributed by SURENDRA_GANGWAR |
C#
// C# program to find distance// between two nodes using LCAusing System;using System.Collections.Generic;class GFG{ static readonly int MAX = 1000; // log2(MAX) static readonly int log = 10; // Array to store the level // of each node static int[] level = new int[MAX]; static int[,] lca = new int[MAX,log]; static int[,] dist = new int[MAX,log]; // List to store tree static List<List<int[]> > graph = new List<List<int[]>>(); static void addEdge(int u, int v, int cost) { graph[u].Add(new int[]{ v, cost }); graph[v].Add(new int[]{ u, cost }); } // Pre-Processing to calculate // values of lca[,], dist[,] static void dfs(int node, int parent, int h, int cost) { // Using recursion formula to // calculate the values // of lca[,] lca[node, 0] = parent; // Storing the level of // each node level[node] = h; if (parent != -1) { dist[node, 0] = cost; } for(int i = 1; i < log; i++) { if (lca[node, i - 1] != -1) { // Using recursion formula to // calculate the values of // lca[,] and dist[,] lca[node, i] = lca[lca[node, i - 1], i - 1]; dist[node, i] = dist[node, i - 1] + dist[lca[node, i - 1], i - 1]; } } foreach(int[] i in graph[node]) { if (i[0] == parent) continue; dfs(i[0], node, h + 1, i[1]); } } // Function to find the distance // between given nodes u and v static void findDistance(int u, int v) { int ans = 0; // The node which is present // farthest from the root node // is taken as v. If u is // farther from root node // then swap the two if (level[u] > level[v]) { int temp = u; u = v; v = temp; } // Finding the ancestor of v // which is at same level as u for(int i = log - 1; i >= 0; i--) { if (lca[v, i] != -1 && level[lca[v, i]] >= level[u]) { // Adding distance of node // v till its 2^i-th ancestor ans += dist[v, i]; v = lca[v, i]; } } // If u is the ancestor of v // then u is the LCA of u and v if (v == u) { Console.WriteLine(ans); } else { // Finding the node closest to the // root which is not the common // ancestor of u and v i.e. a node // x such that x is not the common // ancestor of u and v but lca[x,0] is for(int i = log - 1; i >= 0; i--) { if (lca[v, i] != lca[u, i]) { // Adding the distance // of v and u to // its 2^i-th ancestor ans += dist[u, i] + dist[v, i]; v = lca[v, i]; u = lca[u, i]; } } // Adding the distance of u and v // to its first ancestor ans += dist[u, 0] + dist[v, 0]; Console.WriteLine(ans); } } // Driver Code public static void Main(String[] args) { // Number of nodes int n = 5; for(int i = 0; i < MAX; i++) { graph.Add(new List<int[]>()); } // Add edges with their cost addEdge(1, 2, 2); addEdge(1, 3, 3); addEdge(2, 4, 5); addEdge(2, 5, 7); // Initialising lca and dist values // with -1 and 0 respectively for(int i = 1; i <= n; i++) { for(int j = 0; j < log; j++) { lca[i, j] = -1; dist[i, j] = 0; } } // Perform DFS dfs(1, -1, 0, 0); // Query 1: {1, 3} findDistance(1, 3); // Query 2: {2, 3} findDistance(2, 3); // Query 3: {3, 5} findDistance(3, 5); }}// This code is contributed by aashish1995 |
Javascript
<script> // Javascript program to find distance // between two nodes using LCA let MAX = 1000; // log2(MAX) let log = 10; // Array to store the level // of each node let level = new Array(MAX); let lca = new Array(MAX); let dist = new Array(MAX); // Vector to store tree let graph = []; function addEdge(u, v, cost) { graph[u].push([ v, cost ]); graph[v].push([ u, cost ]); } // Pre-Processing to calculate // values of lca[][], dist[][] function dfs(node, parent, h, cost) { // Using recursion formula to // calculate the values // of lca[][] lca[node][0] = parent; // Storing the level of // each node level[node] = h; if (parent != -1) { dist[node][0] = cost; } for(let i = 1; i < log; i++) { if (lca[node][i - 1] != -1) { // Using recursion formula to // calculate the values of // lca[][] and dist[][] lca[node][i] = lca[lca[node][i - 1]][i - 1]; dist[node][i] = dist[node][i - 1] + dist[lca[node][i - 1]][i - 1]; } } for(let i = 0; i < graph[node].length; i++) { if (graph[node][i][0] == parent) continue; dfs(graph[node][i][0], node, h + 1, graph[node][i][1]); } } // Function to find the distance // between given nodes u and v function findDistance(u, v) { let ans = 0; // The node which is present // farthest from the root node // is taken as v. If u is // farther from root node // then swap the two if (level[u] > level[v]) { let temp = u; u = v; v = temp; } // Finding the ancestor of v // which is at same level as u for(let i = log - 1; i >= 0; i--) { if (lca[v][i] != -1 && level[lca[v][i]] >= level[u]) { // Adding distance of node // v till its 2^i-th ancestor ans += dist[v][i]; v = lca[v][i]; } } // If u is the ancestor of v // then u is the LCA of u and v if (v == u) { document.write(ans + "</br>"); } else { // Finding the node closest to the // root which is not the common // ancestor of u and v i.e. a node // x such that x is not the common // ancestor of u and v but lca[x][0] is for(let i = log - 1; i >= 0; i--) { if (lca[v][i] != lca[u][i]) { // Adding the distance // of v and u to // its 2^i-th ancestor ans += dist[u][i] + dist[v][i]; v = lca[v][i]; u = lca[u][i]; } } // Adding the distance of u and v // to its first ancestor ans += dist[u][0] + dist[v][0]; document.write(ans + "</br>"); } } // Number of nodes let n = 5; for(let i = 0; i < MAX; i++) { graph.push([]); } // Add edges with their cost addEdge(1, 2, 2); addEdge(1, 3, 3); addEdge(2, 4, 5); addEdge(2, 5, 7); // Initialising lca and dist values // with -1 and 0 respectively for(let i = 1; i <= n; i++) { lca[i] = new Array(log); dist[i] = new Array(log); for(let j = 0; j < log; j++) { lca[i][j] = -1; dist[i][j] = 0; } } // Perform DFS dfs(1, -1, 0, 0); // Query 1: {1, 3} findDistance(1, 3); // Query 2: {2, 3} findDistance(2, 3); // Query 3: {3, 5} findDistance(3, 5);// This code is contributed by decode2207.</script> |
Output:
3 5 12
Time Complexity: The time taken in pre-processing is O(N logN) and every query takes O(logN) time. Therefore, overall time complexity of the solution is O(N logN).
Space Complexity: O(N*log(N))
We are storing the LCA and distance of all the nodes in two 2-D arrays.
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