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79 lines
2.2 KiB
79 lines
2.2 KiB
/**
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* Quick select n-th element in an array.
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*
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* Note: it will change the elements placement in array.
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*
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* @module echarts/data/quickSelect
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* @author Yi Shen(https://github.com/pissang)
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*/
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define(function (require) {
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function defaultCompareFunc(a, b) {
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return a - b;
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}
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function swapElement(list, idx0, idx1) {
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var tmp = list[idx0];
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list[idx0] = list[idx1];
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list[idx1] = tmp;
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}
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function select(list, left, right, nth, compareFunc) {
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var pivotIdx = left;
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while (right > left) {
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var pivotIdx = Math.round((right + left) / 2);
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var pivotValue = list[pivotIdx];
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// Swap pivot to the end
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swapElement(list, pivotIdx, right);
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pivotIdx = left;
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for (var i = left; i <= right - 1; i++) {
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if (compareFunc(pivotValue, list[i]) >= 0) {
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swapElement(list, i, pivotIdx);
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pivotIdx++;
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}
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}
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swapElement(list, right, pivotIdx);
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if (pivotIdx === nth) {
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return pivotIdx;
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} else if (pivotIdx < nth) {
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left = pivotIdx + 1;
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} else {
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right = pivotIdx - 1;
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}
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}
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// Left == right
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return left;
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}
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/**
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* @alias module:echarts/data/quickSelect
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* @param {Array} list
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* @param {number} [left]
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* @param {number} [right]
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* @param {number} nth
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* @param {Function} [compareFunc]
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* @example
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* var quickSelect = require('echarts/data/quickSelect');
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* var list = [5, 2, 1, 4, 3]
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* quickSelect(list, 3);
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* quickSelect(list, 0, 3, 1, function (a, b) {return a - b});
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*
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* @return {number}
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*/
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function quickSelect(list, left, right, nth, compareFunc) {
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if (arguments.length <= 3) {
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nth = left;
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if (arguments.length == 2) {
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compareFunc = defaultCompareFunc;
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} else {
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compareFunc = right;
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}
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left = 0;
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right = list.length - 1;
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}
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return select(list, left, right, nth, compareFunc);
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}
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return quickSelect;
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});
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