sorted-btree/extended/union.js

A sorted list of key-value pairs in a fast, typed in-memory B+ tree with a powerful API.

"use strict";
Object.defineProperty(exports, "__esModule", { value: true });
var shared_1 = require("./shared");
var decompose_1 = require("./decompose");
/**
 * Efficiently unions two trees, reusing subtrees wherever possible without mutating either input.
 *
 * Complexity is O(N + M) when the trees overlap heavily, and additionally bounded by O(log(N + M) * D)
 * where `D` is the number of disjoint key ranges, because disjoint subtrees are skipped entirely.
 * In practice, that means for keys of random distribution the performance is linear and for keys with significant
 * numbers of non-overlapping key ranges it is much faster.
 * @param treeA First tree to union.
 * @param treeB Second tree to union.
 * @param combineFn Called for keys that appear in both trees. Return the desired value, or
 *        `undefined` to omit the key from the result. Note: symmetric difference can be achieved by always returning `undefined`.
 * @returns A new BTree that contains the unioned key/value pairs.
 * @throws Error if the trees were created with different comparators or max node sizes.
 */
function union(treeA, treeB, combineFn) {
    if (treeA === treeB)
        return treeA.clone();
    var _treeA = treeA;
    var _treeB = treeB;
    var branchingFactor = (0, shared_1.checkCanDoSetOperation)(_treeA, _treeB, false);
    if (_treeA._root.size() === 0)
        return treeB.clone();
    if (_treeB._root.size() === 0)
        return treeA.clone();
    // Decompose both trees into disjoint subtrees leaves.
    // As many of these as possible will be reused from the original trees, and the remaining
    // will be leaves that are the result of merging intersecting leaves.
    var decomposed = (0, decompose_1.decompose)(_treeA, _treeB, combineFn);
    var constructor = treeA.constructor;
    return (0, decompose_1.buildFromDecomposition)(constructor, branchingFactor, decomposed, _treeA._compare, _treeA._maxNodeSize);
}
exports.default = union;