排序和合并数组

Question

我必须合并两个数组并根据比较按创建的值排序。我不想使用任何内置的 js 函数，例如 sort。我尝试使用 while 循环，但无法找出确切的解决方案。这是我的示例代码：

function merge(a, b, n, m)  
{  
    res = []; 
    i = 0; j = 0; k = 0;  
    while(i < n && j < m) {
        if(a[i]['created'] < b[j]['created']) {
            res.push(a[i]);
            i++;
        } else {
            res.push(b[j]);
            j++;
        }        
    }

    while(i < n) {
        res.push(a[i]);
        i++;
    }

    while(j < m) {
        res.push(b[j]);
        j++;
    }
    return res;  
}  

a = [{'title':'title1', 'created':'18'},{'title':'title2', 'created':'16'},{'title':'title3', 'created':'20'}];  
b = [{'title':'title4','created':'17'},{'title':'title5','created':'19'}];  
n = a.length;  
m = b.length;  

var endResult = merge(a, b, n, m);  
console.log(endResult);

我的预期输出应该如下：

[{'title':'title2', 'created':'16'},{'title':'title4','created':'17'},{'title':'title1', 'created':'18'},{'title':'title5','created':'19'},{'title':'title3', 'created':'20'}];

请让我知道我在这里错过了什么。

注意：我不想使用像 sort() 这样的内置 Javascript 函数。我必须根据特定的业务逻辑对值进行排序，我将在弄清楚基本排序后实现。

Answer 1

一个简单的 O(n^2) 解决方案是遍历所有元素以寻找最小值，然后再次遍历它们以寻找第二低的值，等等。

function mergeSort(a, b) {
    var array = a.concat(b);
    var length = array.length;
    var results = [];
    while(results.length < length) {
	var currentLowest = 0;
	for(var i = 1; i < array.length; i++) {
	    if(array[i].created < array[currentLowest].created) {
		currentLowest = i;
	    }
	}
	results.push(array[currentLowest]);
	array.splice(currentLowest,1);
    }
    return results;
}

a = [{'title':'title1', 'created':'18'},{'title':'title2', 'created':'16'},{'title':'title3', 'created':'20'}];  
b = [{'title':'title4','created':'17'},{'title':'title5','created':'19'}];

var endResult = mergeSort(a,b);
document.getElementsByTagName('p')[0].innerHTML = JSON.stringify(endResult);

<p></p>

Answer 2

您可以采用嵌套循环并在 concat 之后对数组进行排序。

function sort(array) {
    var sorted = [],
        i = array.length,
        j;

    while (i--) {
        for (j = 0; j < sorted.length; j++) {
            if (array[i].created < sorted[j].created) {
                break;
            }
        }
        sorted.splice(j, 0, array[i]);
    }
    return sorted;
}

var a = [{ title: 'title1', created: '18' }, { title: 'title2', created: '16' }, { title: 'title3', created: '20' }],
    b = [{ title: 'title4', created: '17' }, { title: 'title5', created: '19'}],
    result = sort(a.concat(b));

console.log(result);

.as-console-wrapper { max-height: 100% !important; top: 0; }

Answer 3

这似乎运作良好，虽然我无法说出它的速度。

  const arr1 = [111,2,300,50,6,71,9];
  const arr2 = [122,8,40,29,611,74,1];
  // Combines the two arrays into one
  const unsorted = arr1.concat(arr2);
  const sorted = [];

  for(i = 0; i < unsorted.length; i++){
    // Adds all elements from the unsorted array to the destination (sorted) array
    insert(unsorted[i], sorted);
  }
  console.log(sorted);

  function insert(item, arr){
    // Adds the first item automatically
    if(arr.length == 0){
      arr.push(item); 
      return; 
    }
    for(let i = 0; i < arr.length; i++){
      if(i + 1 == arr.length){
        // Adds the item at the end of the array because it's so big 
        arr.push(item);
        break;
      }

      else if(item < arr[i]){
        // Adds the item at the appropriate position in the sorted array
        arr.splice(i, 0, item);
        break;
      }
    }
  }

Answer 4

使用内置的sort 和concat 函数很容易做到这一点。

自定义逻辑可以提供给比较器函数。很难想象任何必需的排序都不能以这种方式完成。

// `comparator` contains your custom business logic.  Return a negative number if `a`
// is smaller than `b`, a positive one if it's larger, and 0 if they're equal.

const mergeAndSort = (comparator) => (a, b) => a.concat(b).sort(comparator)

const myComparator = (a, b) => {
  return Number(a.created) - Number(b.created)  // or just `a.created - `b.created`
}

const a = [{ title: 'title1', created: '18' }, { title: 'title2', created: '16' }, { title: 'title3', created: '20' }],
      b = [{ title: 'title4', created: '17' }, { title: 'title5', created: '19'}]

console.log(mergeAndSort(myComparator)(a, b))

这是学习如何编写排序算法的尝试吗？如果没有，那么我会采用这样的方法。