Question

我正在开设关于算法的可汗学院的课程我经常试着自己弄清楚这些例子，但这次我真的没有得到它。练习位于：Khan Academy Merge Sort Exercise 因此，我要求善良的人为我解决这个问题，因为我已经陷入困境，这是我第一次无法实现某些目标。我确信我会理解这个算法（我想我会这样做，但是在看似解决方案后，它给我的实施错误，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);

＆＃13;

// 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);

＆＃13;

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p数组的开始。

我不确定r > 1正在尝试做什么。因此它不会得到满足并递归执行，直到它耗尽堆栈空间

// 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);

合并排序JavaScript实现

1 个答案: