echarts quickSelect 源码
echarts quickSelect 代码
文件路径：/src/util/quickSelect.ts
/*
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing,
* software distributed under the License is distributed on an
* "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
* KIND, either express or implied. See the License for the
* specific language governing permissions and limitations
* under the License.
*/
/**
* Quick select n-th element in an array.
*
* Note: it will change the elements placement in array.
*/
type CompareFunc<T> = (a: T, b: T) => number;
function defaultCompareFunc(a: any, b: any): any {
return a - b;
}
function swapElement<T>(arr: T[], idx0: number, idx1: number) {
const tmp = arr[idx0];
arr[idx0] = arr[idx1];
arr[idx1] = tmp;
}
function select<T>(arr: T[], left: number, right: number, nth: number, compareFunc: CompareFunc<T>): number {
let pivotIdx = left;
let pivotValue;
while (right > left) {
pivotIdx = Math.round((right + left) / 2);
pivotValue = arr[pivotIdx];
// Swap pivot to the end
swapElement(arr, pivotIdx, right);
pivotIdx = left;
for (let i = left; i <= right - 1; i++) {
if (compareFunc(pivotValue, arr[i]) >= 0) {
swapElement(arr, i, pivotIdx);
pivotIdx++;
}
}
swapElement(arr, right, pivotIdx);
if (pivotIdx === nth) {
return pivotIdx;
}
else if (pivotIdx < nth) {
left = pivotIdx + 1;
}
else {
right = pivotIdx - 1;
}
}
// Left == right
return left;
}
/**
* @example
* let arr = [5, 2, 1, 4, 3]
* quickSelect(arr, 3);
* quickSelect(arr, 0, 3, 1, function (a, b) {return a - b});
*
* @return {number}
*/
function quickSelect<T>(arr: T[], nth: number, compareFunc: CompareFunc<T>): number;
function quickSelect<T>(arr: T[], nth: number, left: number, right: number, compareFunc: CompareFunc<T>): number;
function quickSelect<T>(
arr: T[], left: number, right: number | CompareFunc<T>, nth?: number, compareFunc?: CompareFunc<T>
): number {
if (arguments.length <= 3) {
nth = left;
if (arguments.length === 2) {
compareFunc = defaultCompareFunc;
}
else {
compareFunc = right as CompareFunc<T>;
}
left = 0;
right = arr.length - 1;
}
return select(arr, left, right as number, nth, compareFunc);
}
export default quickSelect;
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