diff --git a/disjoint_sets.java b/disjoint_sets.java new file mode 100644 index 000000000..03bce1a97 --- /dev/null +++ b/disjoint_sets.java @@ -0,0 +1,116 @@ +import java.io.*; +import java.util.*; + +class DisjointUnionSets { + int[] rank, parent; + int n; + + // Constructor + public DisjointUnionSets(int n) + { + rank = new int[n]; + parent = new int[n]; + this.n = n; + makeSet(); + } + + // Creates n sets with single item in each + void makeSet() + { + for (int i = 0; i < n; i++) { + // Initially, all elements are in + // their own set. + parent[i] = i; + } + } + + // Returns representative of x's set + int find(int x) + { + // Finds the representative of the set + // that x is an element of + if (parent[x] != x) { + // if x is not the parent of itself + // Then x is not the representative of + // his set, + parent[x] = find(parent[x]); + + // so we recursively call Find on its parent + // and move i's node directly under the + // representative of this set + } + + return parent[x]; + } + + // Unites the set that includes x and the set + // that includes x + void union(int x, int y) + { + // Find representatives of two sets + int xRoot = find(x), yRoot = find(y); + + // Elements are in the same set, no need + // to unite anything. + if (xRoot == yRoot) + return; + + // If x's rank is less than y's rank + if (rank[xRoot] < rank[yRoot]) + + // Then move x under y so that depth + // of tree remains less + parent[xRoot] = yRoot; + + // Else if y's rank is less than x's rank + else if (rank[yRoot] < rank[xRoot]) + + // Then move y under x so that depth of + // tree remains less + parent[yRoot] = xRoot; + + else // if ranks are the same + { + // Then move y under x (doesn't matter + // which one goes where) + parent[yRoot] = xRoot; + + // And increment the result tree's + // rank by 1 + rank[xRoot] = rank[xRoot] + 1; + } + } +} + +// Driver code +public class Main { + public static void main(String[] args) + { + // Let there be 5 persons with ids as + // 0, 1, 2, 3 and 4 + int n = 5; + DisjointUnionSets dus = + new DisjointUnionSets(n); + + // 0 is a friend of 2 + dus.union(0, 2); + + // 4 is a friend of 2 + dus.union(4, 2); + + // 3 is a friend of 1 + dus.union(3, 1); + + // Check if 4 is a friend of 0 + if (dus.find(4) == dus.find(0)) + System.out.println("Yes"); + else + System.out.println("No"); + + // Check if 1 is a friend of 0 + if (dus.find(1) == dus.find(0)) + System.out.println("Yes"); + else + System.out.println("No"); + } +}