Created
February 17, 2017 18:38
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Count Inversions in an array
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| function MergSortEntry(arr){ | |
| // console.log(arr) | |
| let tempArr = []; | |
| let i = MergeSort(arr, tempArr, 0, arr.length - 1) | |
| //console.log(arr) | |
| return i | |
| } | |
| function MergeSort(arr, tempArr, leftStart, rightEnd ){ | |
| let invCount = 0; | |
| if( rightEnd > leftStart ){ | |
| let mid = parseInt( (leftStart + rightEnd) / 2 ); | |
| invCount += MergeSort(arr, tempArr, leftStart, mid); | |
| invCount += MergeSort(arr, tempArr, mid + 1, rightEnd); | |
| invCount += MergeAndCount(arr, tempArr, leftStart, mid + 1, rightEnd); | |
| } | |
| return invCount; | |
| } | |
| function MergeAndCount(arr, tempArr, leftIdx, midIdx, rightIdx){ | |
| let invCount = 0; | |
| let leftNewIdx = leftIdx // idx for left sub array | |
| let rightNewIdx = midIdx // idx for right sub array | |
| let tempIdx = leftIdx // idx for temp array | |
| while ( ( leftNewIdx <= midIdx - 1) && ( rightNewIdx <= rightIdx ) ){ | |
| if( arr[leftNewIdx] <= arr[rightNewIdx]){ | |
| tempArr[tempIdx] = arr[leftNewIdx]; | |
| leftNewIdx++; | |
| }else{ | |
| tempArr[tempIdx] = arr[rightNewIdx]; | |
| rightNewIdx++; | |
| invCount += (midIdx - leftNewIdx); | |
| // console.log('--- invcount temp--', invCount += (midIdx - leftNewIdx) ) | |
| } | |
| tempIdx++; | |
| } | |
| while( leftNewIdx <= midIdx - 1 ){ | |
| tempArr[tempIdx] = arr[leftNewIdx]; | |
| leftNewIdx++; | |
| tempIdx++; | |
| } | |
| while( rightNewIdx <= rightIdx ){ | |
| tempArr[tempIdx] = arr[rightNewIdx]; | |
| rightNewIdx++; | |
| tempIdx++; | |
| } | |
| for( var i = leftIdx; i <= rightIdx; i++){ | |
| arr[i] = tempArr[i]; | |
| } | |
| return invCount; | |
| } | |
| var a = [34, 203, 3, 746, 200, 984, 198, 764, 9]; | |
| var b = [2,1,3,1,2] | |
| //console.log( MergSortEntry(b)); | |
| //console.log( MergSortEntry(a)); |
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