fix: rangeByRank return types — TreeMap returns entries, TreeSet returns keys

- TreeMap.rangeByRank → Array<[K, V | undefined]> (consistent with rangeSearch)
- TreeMultiMap.rangeByRank → Array<[K, V[]]>
- TreeSet.rangeByRank → K[] (consistent with rangeSearch)
- TreeMultiSet.rangeByRank → K[]
- Add TreeMap rangeByRank test

Author: zrwusa

src/data-structures/binary-tree/tree-map.ts

@@ -4471,8 +4471,11 @@ export class TreeMap<K = any, V = any, R = [K, V]> implements Iterable<[K, V | u
  *       // Page 3
  *       console.log(tree.rangeByRank(2 * pageSize, 3 * pageSize - 1)); // [70, 80, 90];
    */
-  rangeByRank(start: number, end: number): (K | undefined)[] {
-    return this.#core.rangeByRank(start, end);
+  rangeByRank(start: number, end: number): Array<[K, V | undefined]> {
+    const keys = this.#core.rangeByRank(start, end);
+    return keys
+      .filter((k): k is K => k !== undefined)
+      .map(k => [k, this.#core.get(k)] as [K, V | undefined]);
   }
 
   /**

src/data-structures/binary-tree/tree-multi-map.ts

@@ -4499,8 +4499,11 @@ export class TreeMultiMap<K = any, V = any, R = any> implements Iterable<[K, V[]
  *       // Page 3
  *       console.log(tree.rangeByRank(2 * pageSize, 3 * pageSize - 1)); // [70, 80, 90];
    */
-  rangeByRank(start: number, end: number): (K | undefined)[] {
-    return this.#core.rangeByRank(start, end);
+  rangeByRank(start: number, end: number): Array<[K, V[]]> {
+    const keys = this.#core.rangeByRank(start, end);
+    return keys
+      .filter((k): k is K => k !== undefined)
+      .map(k => [k, this.#core.get(k) ?? []] as [K, V[]]);
   }
 
     /**

src/data-structures/binary-tree/tree-multi-set.ts

@@ -3305,8 +3305,8 @@ export class TreeMultiSet<K = any, R = K> implements Iterable<K> {
  *       // Page 3
  *       console.log(tree.rangeByRank(2 * pageSize, 3 * pageSize - 1)); // [70, 80, 90];
    */
-  rangeByRank(start: number, end: number): (K | undefined)[] {
-    return this.#core.rangeByRank(start, end);
+  rangeByRank(start: number, end: number): K[] {
+    return this.#core.rangeByRank(start, end).filter((k): k is K => k !== undefined);
   }
 
     /**

src/data-structures/binary-tree/tree-set.ts

@@ -4165,8 +4165,8 @@ export class TreeSet<K = any, R = K> implements Iterable<K> {
  *       // Page 3
  *       console.log(tree.rangeByRank(2 * pageSize, 3 * pageSize - 1)); // [70, 80, 90];
    */
-  rangeByRank(start: number, end: number): (K | undefined)[] {
-    return this.#core.rangeByRank(start, end);
+  rangeByRank(start: number, end: number): K[] {
+    return this.#core.rangeByRank(start, end).filter((k): k is K => k !== undefined);
   }
 
   /**

test/unit/data-structures/binary-tree/bst.order-statistic.test.ts

@@ -330,6 +330,15 @@ describe('Order Statistic Tree', () => {
       expect(map.rank('aaa')).toBe(0);  // before alice
       expect(map.rank('bbb')).toBe(1);  // between alice and bob
     });
+
+    it('rangeByRank should return entries [key, value]', () => {
+      const map = new TreeMap<string, number>(
+        [['alice', 95], ['bob', 87], ['charlie', 92]],
+        { enableOrderStatistic: true }
+      );
+      const result = map.rangeByRank(0, 1);
+      expect(result).toEqual([['alice', 95], ['bob', 87]]);
+    });
   });
 
   describe('TreeSet', () => {