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array.ts
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array.ts
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type ComparisonFunction<T> = (a: T, b: T) => number;
function compareBigInt(a: string, b: string): number {
const difference = BigInt(a) - BigInt(b);
return parseInt("" + difference);
}
function compareStrings(a: string, b: string): number {
return a.localeCompare(b);
}
export function find<T>(
sortedItems: T[],
targetItem: T,
comparisonFunction: ComparisonFunction<T>,
exactMatch = true
): T | null {
const index = findIndex(sortedItems, targetItem, comparisonFunction, exactMatch);
return index >= 0 ? sortedItems[index] : null;
}
export function findIndexLTE<T>(
sortedItems: T[],
targetItem: T,
comparisonFunction: ComparisonFunction<T>
): number {
const index = findIndex(sortedItems, targetItem, comparisonFunction, false);
// This is the nearest item, but it may be greater
const item = sortedItems[index];
if (item) {
if (comparisonFunction(targetItem, item) >= 0) {
return index;
} else {
return index - 1;
}
}
return -1;
}
export function findIndexGTE<T>(
sortedItems: T[],
targetItem: T,
comparisonFunction: ComparisonFunction<T>
): number {
const index = findIndex(sortedItems, targetItem, comparisonFunction, false);
// This is the nearest item, but it may be lesser
const item = sortedItems[index];
if (item) {
if (comparisonFunction(targetItem, item) <= 0) {
return index;
} else if (index < sortedItems.length - 1) {
return index + 1;
}
}
return -1;
}
// Note that for non-exact matches to work
// the comparison function should return more fine-grained delta values than the typical -1, 0, or 1.
export function findIndex<T>(
sortedItems: T[],
targetItem: T,
comparisonFunction: ComparisonFunction<T>,
exactMatch = true
): number {
let lowIndex = 0;
let highIndex = sortedItems.length - 1;
let middleIndex = -1;
while (lowIndex <= highIndex) {
middleIndex = (lowIndex + highIndex) >>> 1;
const currentItem = sortedItems[middleIndex];
const value = comparisonFunction(targetItem, currentItem);
if (value === 0) {
return middleIndex;
} else if (value > 0) {
lowIndex = middleIndex + 1;
} else {
highIndex = middleIndex - 1;
}
}
if (exactMatch) {
return -1;
} else {
switch (sortedItems.length) {
case 0:
return -1;
case 1:
return 0;
}
const value = comparisonFunction(targetItem, sortedItems[middleIndex]);
if (value === 0) {
return middleIndex;
} else {
let lowIndex = middleIndex;
let highIndex = middleIndex;
if (value > 0) {
highIndex = Math.min(middleIndex + 1, sortedItems.length - 1);
} else {
lowIndex = Math.max(0, middleIndex - 1);
}
return Math.abs(comparisonFunction(targetItem, sortedItems[lowIndex])) <
Math.abs(comparisonFunction(targetItem, sortedItems[highIndex]))
? lowIndex
: highIndex;
}
}
}
export function findIndexBigInt(
sortedItems: string[],
targetItem: string,
exactMatch = true
): number {
return findIndex<string>(sortedItems, targetItem, compareBigInt, exactMatch);
}
export function findIndexString(sortedItems: string[], targetItem: string): number {
return findIndex<string>(sortedItems, targetItem, compareStrings);
}
export function findInsertIndex<T>(
sortedItems: T[],
item: T,
comparisonFunction: ComparisonFunction<T>
): number {
let lowIndex = 0;
let highIndex = sortedItems.length;
while (lowIndex < highIndex) {
let middleIndex = (lowIndex + highIndex) >>> 1;
const currentItem = sortedItems[middleIndex];
if (comparisonFunction(item, currentItem) > 0) {
lowIndex = middleIndex + 1;
} else {
highIndex = middleIndex;
}
}
return lowIndex;
}
export function insert<T>(
sortedItems: T[],
item: T,
comparisonFunction: ComparisonFunction<T>
): T[] {
const insertAtIndex = findInsertIndex(sortedItems, item, comparisonFunction);
sortedItems.splice(insertAtIndex, 0, item);
return sortedItems;
}
export function insertString(sortedItems: string[], item: string): string[] {
return insert<string>(sortedItems, item, (a, b) => a.localeCompare(b));
}