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- 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];
-
- 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;
- }
- }
-
- return left;
- }
- function quickSelect(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);
- }
- export default quickSelect;
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