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Merge sort implementation in JavaScript.
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function merge(xs, leftStart, leftEnd, rightStart, rightEnd) { | |
var i = leftStart; | |
var j = rightStart; | |
var merged = []; | |
var currentLeft, currentRight; | |
// Merge. | |
while (i <= leftEnd || j <= rightEnd) { | |
currentLeft = xs[i]; | |
currentRight = xs[j]; | |
if ((currentLeft <= currentRight || j > rightEnd) && i <= leftEnd) { | |
merged.push(currentLeft); | |
i++; | |
} else if ((currentLeft > currentRight || i > leftEnd) && j <= rightEnd) { | |
merged.push(currentRight); | |
j++; | |
} | |
} | |
var k; | |
// Update source array. | |
for (k = 0; k <= rightEnd - leftStart; k++) { | |
xs[k + leftStart] = merged[k]; | |
} | |
} | |
function mergeSort0(xs, start, end) { | |
var middle = Math.ceil((end - start) / 2); | |
var leftStart = start; | |
var leftEnd = Math.max(start, middle - 1); | |
var rightEnd = end; | |
var rightStart = Math.min(rightEnd, leftEnd + 1); | |
if (leftStart !== rightEnd) { | |
mergeSort0(xs, leftStart, leftEnd); | |
mergeSort0(xs, rightStart, rightEnd); | |
merge(xs, leftStart, leftEnd, rightStart, rightEnd); | |
} | |
return(xs); | |
} | |
function mergeSort(xs) { | |
if (xs.length <= 1) { | |
return(xs); | |
} | |
return(mergeSort0(xs, 0, xs.length - 1)); | |
} |
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