JS-数组sort方法用的是哪种排序算法|诺禾

说明一下,ECMAScript没有定义使用哪种排序算法,各个浏览器的实现方式会有不同。火狐中使用的是归并排序,下面是Chrome的sort排序算法的实现。

sort方法源码
DEFINE_METHOD(
GlobalArray.prototype,
sort(comparefn) {
CHECK_OBJECT_COERCIBLE(this, “Array.prototype.sort”);

if (!IS_UNDEFINED(comparefn) && !IS_CALLABLE(comparefn)) {
  throw %make_type_error(kBadSortComparisonFunction, comparefn);
}

var array = TO_OBJECT(this);
var length = TO_LENGTH(array.length);
return InnerArraySort(array, length, comparefn);

}
);
这一步看出sort方法调用了InnerArraySort方法,参数是数组,数组长度,比较函数。再看看InnerArraySort方法是如何处理的。

InnerArraySort方法源码
function InnerArraySort(array, length, comparefn) {
// In-place QuickSort algorithm.
// For short (length <= 10) arrays, insertion sort is used for efficiency.

if (!IS_CALLABLE(comparefn)) {
comparefn = function (x, y) {
if (x === y) return 0;
if (%_IsSmi(x) && %_IsSmi(y)) {
return %SmiLexicographicCompare(x, y);
}
x = TO_STRING(x);
y = TO_STRING(y);
if (x == y) return 0;
else return x < y ? -1 : 1;
};
}
function InsertionSort(a, from, to) {

};

function QuickSort(a, from, to) {
var third_index = 0;
while (true) {
// Insertion sort is faster for short arrays.
if (to - from <= 10) {
InsertionSort(a, from, to);
return;
}
if (to - from > 1000) {
third_index = GetThirdIndex(a, from, to);
} else {
third_index = from + ((to - from) >> 1);
}
// Find a pivot as the median of first, last and middle element.
var v0 = a[from];
var v1 = a[to - 1];
var v2 = a[third_index];
var c01 = comparefn(v0, v1);
if (c01 > 0) {
// v1 < v0, so swap them.
var tmp = v0;
v0 = v1;
v1 = tmp;
} // v0 <= v1.
var c02 = comparefn(v0, v2);
if (c02 >= 0) {
// v2 <= v0 <= v1.
var tmp = v0;
v0 = v2;
v2 = v1;
v1 = tmp;
} else {
// v0 <= v1 && v0 < v2
var c12 = comparefn(v1, v2);
if (c12 > 0) {
// v0 <= v2 < v1
var tmp = v1;
v1 = v2;
v2 = tmp;
}
}
// v0 <= v1 <= v2
a[from] = v0;
a[to - 1] = v2;
var pivot = v1;
var low_end = from + 1; // Upper bound of elements lower than pivot.
var high_start = to - 1; // Lower bound of elements greater than pivot.
a[third_index] = a[low_end];
a[low_end] = pivot;

  // From low_end to i are elements equal to pivot.
  // From i to high_start are elements that haven't been compared yet.
  partition: for (var i = low_end + 1; i < high_start; i++) {
    var element = a[i];
    var order = comparefn(element, pivot);
    if (order < 0) {
      a[i] = a[low_end];
      a[low_end] = element;
      low_end++;
    } else if (order > 0) {
      do {
        high_start--;
        if (high_start == i) break partition;
        var top_elem = a[high_start];
        order = comparefn(top_elem, pivot);
      } while (order > 0);
      a[i] = a[high_start];
      a[high_start] = element;
      if (order < 0) {
        element = a[i];
        a[i] = a[low_end];
        a[low_end] = element;
        low_end++;
      }
    }
  }
  if (to - high_start < low_end - from) {
    QuickSort(a, high_start, to);
    to = low_end;
  } else {
    QuickSort(a, from, low_end);
    from = high_start;
  }
}

};

QuickSort(array, 0, num_non_undefined);

return array;
}
这一步最重要的是QuickSort,从代码和注释中可以看出sort使用的是插入排序和快速排序结合的排序算法。数组长度不超过10时,使用插入排序。长度超过10使用快速排序。在数组较短时插入排序更有效率。

问题终于找到了答案,心里又少了一个挂念的问题。

你可能感兴趣的:(js)