Add disjoint set.

Author: trekhleb

src/data-structures/disjoint-set/DisjointSet.js

@@ -25,6 +25,8 @@ export default class DisjointSet {
   }
 
   /**
+   * Find set representation node.
+   *
    * @param {*} itemValue
    * @return {(string|null)}
    */
@@ -42,6 +44,8 @@ export default class DisjointSet {
   }
 
   /**
+   * Union by rank.
+   *
    * @param {*} valueA
    * @param {*} valueB
    * @return {DisjointSet}
@@ -62,7 +66,7 @@ export default class DisjointSet {
     const rootA = this.items[rootKeyA];
     const rootB = this.items[rootKeyB];
 
-    if (rootA.getAncestorsCount() < rootB.getAncestorsCount()) {
+    if (rootA.getRank() < rootB.getRank()) {
       // If rootB's tree is bigger then make rootB to be a new root.
       rootB.addChild(rootA);
 

src/data-structures/disjoint-set/DisjointSetItem.js

@@ -39,25 +39,27 @@ export default class DisjointSetItem {
   }
 
   /**
+   * Rank basically means the number of all ancestors.
+   *
    * @return {number}
    */
-  getAncestorsCount() {
+  getRank() {
     if (this.getChildren().length === 0) {
       return 0;
     }
 
-    let count = 0;
+    let rank = 0;
 
     /** @var {DisjointSetItem} child */
     this.getChildren().forEach((child) => {
       // Count child itself.
-      count += 1;
+      rank += 1;
 
       // Also add all children of current child.
-      count += child.getAncestorsCount();
+      rank += child.getRank();
     });
 
-    return count;
+    return rank;
   }
 
   /**

src/data-structures/disjoint-set/__test__/DisjointSetItem.test.js

@@ -7,7 +7,7 @@ describe('DisjointSetItem', () => {
     const itemC = new DisjointSetItem('C');
     const itemD = new DisjointSetItem('D');
 
-    expect(itemA.getAncestorsCount()).toBe(0);
+    expect(itemA.getRank()).toBe(0);
     expect(itemA.getChildren()).toEqual([]);
     expect(itemA.getKey()).toBe('A');
     expect(itemA.getRoot()).toEqual(itemA);
@@ -17,11 +17,11 @@ describe('DisjointSetItem', () => {
     itemA.addChild(itemB);
     itemD.setParent(itemC);
 
-    expect(itemA.getAncestorsCount()).toBe(1);
-    expect(itemC.getAncestorsCount()).toBe(1);
+    expect(itemA.getRank()).toBe(1);
+    expect(itemC.getRank()).toBe(1);
 
-    expect(itemB.getAncestorsCount()).toBe(0);
-    expect(itemD.getAncestorsCount()).toBe(0);
+    expect(itemB.getRank()).toBe(0);
+    expect(itemD.getRank()).toBe(0);
 
     expect(itemA.getChildren().length).toBe(1);
     expect(itemC.getChildren().length).toBe(1);
@@ -50,9 +50,9 @@ describe('DisjointSetItem', () => {
     expect(itemC.isRoot()).toBeFalsy();
     expect(itemD.isRoot()).toBeFalsy();
 
-    expect(itemA.getAncestorsCount()).toEqual(3);
-    expect(itemB.getAncestorsCount()).toEqual(0);
-    expect(itemC.getAncestorsCount()).toEqual(1);
+    expect(itemA.getRank()).toEqual(3);
+    expect(itemB.getRank()).toEqual(0);
+    expect(itemC.getRank()).toEqual(1);
   });
 
   it('should do basic manipulation with disjoint set item with custom key extractor', () => {
@@ -65,7 +65,7 @@ describe('DisjointSetItem', () => {
     const itemC = new DisjointSetItem({ key: 'C', value: 3 }, keyExtractor);
     const itemD = new DisjointSetItem({ key: 'D', value: 4 }, keyExtractor);
 
-    expect(itemA.getAncestorsCount()).toBe(0);
+    expect(itemA.getRank()).toBe(0);
     expect(itemA.getChildren()).toEqual([]);
     expect(itemA.getKey()).toBe('A');
     expect(itemA.getRoot()).toEqual(itemA);
@@ -75,11 +75,11 @@ describe('DisjointSetItem', () => {
     itemA.addChild(itemB);
     itemD.setParent(itemC);
 
-    expect(itemA.getAncestorsCount()).toBe(1);
-    expect(itemC.getAncestorsCount()).toBe(1);
+    expect(itemA.getRank()).toBe(1);
+    expect(itemC.getRank()).toBe(1);
 
-    expect(itemB.getAncestorsCount()).toBe(0);
-    expect(itemD.getAncestorsCount()).toBe(0);
+    expect(itemB.getRank()).toBe(0);
+    expect(itemD.getRank()).toBe(0);
 
     expect(itemA.getChildren().length).toBe(1);
     expect(itemC.getChildren().length).toBe(1);
@@ -108,8 +108,8 @@ describe('DisjointSetItem', () => {
     expect(itemC.isRoot()).toBeFalsy();
     expect(itemD.isRoot()).toBeFalsy();
 
-    expect(itemA.getAncestorsCount()).toEqual(3);
-    expect(itemB.getAncestorsCount()).toEqual(0);
-    expect(itemC.getAncestorsCount()).toEqual(1);
+    expect(itemA.getRank()).toEqual(3);
+    expect(itemB.getRank()).toEqual(0);
+    expect(itemC.getRank()).toEqual(1);
   });
 });