quickSelect.js
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/*
* 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.
*
* @module echarts/core/quickSelect
* @author Yi Shen(https://github.com/pissang)
*/
function defaultCompareFunc(a, b) {
return a - b;
}
function swapElement(arr, idx0, idx1) {
var tmp = arr[idx0];
arr[idx0] = arr[idx1];
arr[idx1] = tmp;
}
function select(arr, left, right, nth, compareFunc) {
var pivotIdx = left;
var 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 (var 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;
}
/**
* @alias module:echarts/core/quickSelect
* @param {Array} arr
* @param {number} [left]
* @param {number} [right]
* @param {number} nth
* @param {Function} [compareFunc]
* @example
* var quickSelect = require('echarts/core/quickSelect');
* var arr = [5, 2, 1, 4, 3]
* quickSelect(arr, 3);
* quickSelect(arr, 0, 3, 1, function (a, b) {return a - b});
*
* @return {number}
*/
export default function (arr, left, right, nth, compareFunc) {
if (arguments.length <= 3) {
nth = left;
if (arguments.length === 2) {
compareFunc = defaultCompareFunc;
}
else {
compareFunc = right;
}
left = 0;
right = arr.length - 1;
}
return select(arr, left, right, nth, compareFunc);
}