diff --git a/docs/index.d.ts b/docs/index.d.ts
index 7dc08f3..c71c69e 100644
--- a/docs/index.d.ts
+++ b/docs/index.d.ts
@@ -94,6 +94,9 @@ export const examples: {
     readonly flatten: 'examples/jsonDiff.ts';
     readonly unflatten: 'examples/jsonDiff.ts';
     readonly paginate: 'examples/pagination.ts';
+    readonly diffTree: 'examples/treeDiff.ts';
+    readonly applyTreeDiff: 'examples/treeDiff.ts';
+    readonly UnionFind: 'examples/graph.ts';
   };
   readonly performance: {
     readonly debounce: 'examples/requestDedup.ts';
@@ -2926,6 +2929,20 @@ export function groupBy<T>(
   key: keyof T | ((item: T) => string)
 ): Record<string, T[]>;
 
+/**
+ * Disjoint Set Union (Union-Find) with path compression and union by size.
+ * Use for: connectivity queries, Kruskal MST, clustering.
+ * Import: data/unionFind.ts
+ */
+export class UnionFind<T = number> {
+  constructor(elements?: Iterable<T>);
+  makeSet(x: T): void;
+  find(x: T): T;
+  union(a: T, b: T): boolean;
+  connected(a: T, b: T): boolean;
+  size(x: T): number;
+}
+
 // ============================================================================
 // 📈 GRAPH ALGORITHMS
 // ============================================================================
diff --git a/src/data/unionFind.ts b/src/data/unionFind.ts
new file mode 100644
index 0000000..f1136c6
--- /dev/null
+++ b/src/data/unionFind.ts
@@ -0,0 +1,60 @@
+/**
+ * Disjoint Set Union (Union-Find) with path compression and union by size.
+ * Useful for: connectivity queries, Kruskal MST, clustering.
+ */
+export class UnionFind<T = number> {
+  private parent = new Map<T, T>();
+  private compSize = new Map<T, number>();
+
+  constructor(elements?: Iterable<T>) {
+    if (elements) {
+      for (const el of elements) {
+        this.makeSet(el);
+      }
+    }
+  }
+
+  makeSet(x: T): void {
+    if (!this.parent.has(x)) {
+      this.parent.set(x, x);
+      this.compSize.set(x, 1);
+    }
+  }
+
+  find(x: T): T {
+    if (!this.parent.has(x)) this.makeSet(x);
+    const direct = this.parent.get(x);
+    let p: T = direct === undefined ? x : (direct as T);
+    if (p !== x) {
+      p = this.find(p);
+      this.parent.set(x, p);
+    }
+    return p;
+  }
+
+  union(a: T, b: T): boolean {
+    let ra = this.find(a);
+    let rb = this.find(b);
+    if (ra === rb) return false;
+    const sa = this.compSize.get(ra)!;
+    const sb = this.compSize.get(rb)!;
+    if (sa < sb) {
+      const tmp = ra;
+      ra = rb;
+      rb = tmp;
+    }
+    // attach rb under ra
+    this.parent.set(rb, ra);
+    this.compSize.set(ra, sa + sb);
+    this.compSize.delete(rb);
+    return true;
+  }
+
+  connected(a: T, b: T): boolean {
+    return this.find(a) === this.find(b);
+  }
+
+  size(x: T): number {
+    return this.compSize.get(this.find(x)) ?? 1;
+  }
+}
diff --git a/src/index.ts b/src/index.ts
index 2d44e46..ab88224 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -94,6 +94,7 @@ export const examples = {
     paginate: 'examples/pagination.ts',
     diffTree: 'examples/treeDiff.ts',
     applyTreeDiff: 'examples/treeDiff.ts',
+    UnionFind: 'examples/graph.ts',
   },
   performance: {
     debounce: 'examples/requestDedup.ts',
@@ -412,7 +413,6 @@ export { satCollision } from './spatial/sat.js';
  */
 export { circleRayIntersection } from './spatial/circleRay.js';
 /**
-<<<<<<< HEAD
  * Fast circle-circle overlap test.
  *
  * Example file: examples/circle.ts
@@ -430,7 +430,7 @@ export { circleAabbCollision } from './spatial/circleCollision.js';
  * Example file: examples/circle.ts
  */
 export { circleSegmentIntersection } from './spatial/circleCollision.js';
-=======
+/**
  * Ray vs. segment intersection test returning closest hit.
  *
  * Example file: examples/raycast.ts
@@ -442,7 +442,6 @@ export { raycastSegment } from './spatial/raycast.js';
  * Example file: examples/raycast.ts
  */
 export { raycastAabb } from './spatial/raycast.js';
->>>>>>> 83f962b (feat(spatial): add raycasting utilities (raycastSegment, raycastAabb); docs + tests + example)
 
 /**
  * Continuous swept AABB collision detection for moving boxes.
@@ -1021,6 +1020,12 @@ export type {
  * Tree diff helpers for hierarchical data.
  */
 export { diffTree, applyTreeDiff } from './data/treeDiff.js';
+/**
+ * Disjoint Set Union (Union-Find) with path compression and union by size.
+ *
+ * Example file: examples/graph.ts
+ */
+export { UnionFind } from './data/unionFind.js';
 
 export type {
   TreeNode,
diff --git a/tests/index.test.ts b/tests/index.test.ts
index dcf120e..cb04ce9 100644
--- a/tests/index.test.ts
+++ b/tests/index.test.ts
@@ -123,6 +123,7 @@ describe('package entry point', () => {
       | 'paginate'
       | 'diffTree'
       | 'applyTreeDiff'
+      | 'UnionFind'
     >();
 
     expectTypeOf<ExampleName<'search'>>().toEqualTypeOf<
diff --git a/tests/unionFind.test.ts b/tests/unionFind.test.ts
new file mode 100644
index 0000000..73953c5
--- /dev/null
+++ b/tests/unionFind.test.ts
@@ -0,0 +1,26 @@
+import { describe, it, expect } from 'vitest';
+import { UnionFind } from '../src/index.js';
+
+describe('UnionFind', () => {
+  it('unions and finds components for numbers', () => {
+    const uf = new UnionFind([0, 1, 2, 3, 4]);
+    uf.union(0, 1);
+    uf.union(2, 3);
+    expect(uf.connected(0, 1)).toBe(true);
+    expect(uf.connected(0, 2)).toBe(false);
+    uf.union(1, 2);
+    expect(uf.connected(0, 3)).toBe(true);
+    expect(uf.size(0)).toBe(4);
+    expect(uf.size(4)).toBe(1);
+  });
+
+  it('supports string keys', () => {
+    const uf = new UnionFind<string>(['a', 'b', 'c']);
+    uf.union('a', 'b');
+    expect(uf.connected('a', 'b')).toBe(true);
+    expect(uf.connected('a', 'c')).toBe(false);
+    uf.makeSet('d');
+    expect(uf.size('d')).toBe(1);
+  });
+});
+