合并排序 JavaScript 实现 [关闭]

Question

我正在学习可汗学院的算法课程。
我通常会尝试自己找出示例，但这次我真的不明白。练习在：Khan Academy Merge Sort Exercise.
所以我请一个好心的人为我解决这个练习，因为我被卡住了，这是我第一次无法实现某些东西。我确信我会在解决方案之后理解该算法（我想我会，但它在实现时给了我错误，所以显然我不理解）。
这是我到目前为止所做的代码：

// Takes in an array that has two sorted subarrays,
//  from [p..q] and [q+1..r], and merges the array
var merge = function(array, p, q, r) {
    // This code has been purposefully obfuscated,
    //  as you'll write it yourself in next challenge.
    var a=[],b=[],c=p,d,e;for(d=0;c<=q;d++,c++){a[d]=array[c];}for(e=0;c<=r;e++,c++){b[e]=array[c];}c=p;for(e=d=0;d<a.length&&e<b.length;){if(a[d]<b[e]){array[c]=a[d];d++;} else {array[c]=b[e]; e++;}c++; }for(;d<a.length;){array[c]=a[d];d++;c++;}for(;e<b.length;){array[c]=b[e];e++;c++;}
};


// Takes in an array and recursively merge sorts it
var mergeSort = function(array, p, r) {
    if(r > 1) {
        var q = Math.floor((p + r) / 2);
        mergeSort(array,p,q);
        mergeSort(array,q+1,r);
        merge(array, p, q, r);
    }

};

var array = [14, 7, 3, 12, 9, 11, 6, 2];
console.log(''+array);
mergeSort(array, 0, array.length-1);
console.log("Array after sorting: " + array);

// Takes in an array that has two sorted subarrays,
    //  from [p..q] and [q+1..r], and merges the array
    var merge = function(array, p, q, r) {
        // This code has been purposefully obfuscated,
        //  as you'll write it yourself in next challenge.
        var a=[],b=[],c=p,d,e;for(d=0;c<=q;d++,c++){a[d]=array[c];}for(e=0;c<=r;e++,c++){b[e]=array[c];}c=p;for(e=d=0;d<a.length&&e<b.length;){if(a[d]<b[e]){array[c]=a[d];d++;} else {array[c]=b[e]; e++;}c++; }for(;d<a.length;){array[c]=a[d];d++;c++;}for(;e<b.length;){array[c]=b[e];e++;c++;}
    };
    
    
    // Takes in an array and recursively merge sorts it
    var mergeSort = function(array, p, r) {
        if(r > 1) {
            var q = Math.floor((p + r) / 2);
            mergeSort(array,p,q);
            mergeSort(array,q+1,r);
            merge(array, p, q, r);
        }
        
    };
    
    var array = [14, 7, 3, 12, 9, 11, 6, 2];
    console.log(''+array);
    mergeSort(array, 0, array.length-1);
    console.log("Array after sorting: " + array);

Answer 1

它与if 条件有关

if 条件实现的是检查数组末尾的r 是否大于数组开头的p。

我不确定r > 1 想要做什么。因此它不会得到满足并递归执行，直到它用完堆栈空间

// Takes in an array that has two sorted subarrays,
//  from [p..q] and [q+1..r], and merges the array
var merge = function(array, p, q, r) {
  // This code has been purposefully obfuscated,
  //  as you'll write it yourself in next challenge.
  var a = [],
    b = [],
    c = p,
    d, e;
  for (d = 0; c <= q; d++, c++) {
    a[d] = array[c];
  }
  for (e = 0; c <= r; e++, c++) {
    b[e] = array[c];
  }
  c = p;
  for (e = d = 0; d < a.length && e < b.length;) {
    if (a[d] < b[e]) {
      array[c] = a[d];
      d++;
    } else {
      array[c] = b[e];
      e++;
    }
    c++;
  }
  for (; d < a.length;) {
    array[c] = a[d];
    d++;
    c++;
  }
  for (; e < b.length;) {
    array[c] = b[e];
    e++;
    c++;
  }
};


// Takes in an array and recursively merge sorts it
var mergeSort = function(array, p, r) {
  if (r > p) {
    var q = Math.floor((p + r) / 2);
    mergeSort(array, p, q);
    mergeSort(array, q + 1, r);
    merge(array, p, q, r);
  }

};

var array = [14, 7, 3, 12, 9, 11, 6, 2];
console.log('' + array);
mergeSort(array, 0, array.length - 1);
console.log("Array after sorting: " + array);