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prefix-tree.ts
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prefix-tree.ts
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import { NodeType, Node, Leaf, TableRow } from "../types";
export function buildTree(str: string) {
const frequencyMap: Record<number, number> = {};
str.split("").forEach((byte) => {
frequencyMap[byte.charCodeAt(0)] =
(frequencyMap[byte.charCodeAt(0)] || 0) + 1;
});
const sortedKeys = Object.keys(frequencyMap).sort((a, b) => {
return frequencyMap[parseInt(a)] - frequencyMap[parseInt(b)];
});
const nodes: Array<Node | Leaf> = sortedKeys.map((key) => {
return new Leaf(parseInt(key), frequencyMap[parseInt(key)]);
});
while (nodes.length > 1) {
const node0 = nodes.shift();
const node1 = nodes.shift();
const newNode = new Node(
node0!,
node1!,
(node0?.count || 0) + (node1?.count || 0)
);
nodes.push(newNode);
nodes.sort((a, b) => a.count - b.count);
}
return nodes[0];
}
export function buildTable(
node: NodeType,
path: number[] = []
): Array<TableRow> {
if (node instanceof Node) {
// is node
const left = buildTable(node.left, path.concat([0]));
const right = buildTable(node.right, path.concat([1]));
return left.concat(right);
} else {
// is leaf
return [new TableRow(node.byte, path)];
}
}