如何在JavaScript中实现二进制搜索 [英] How to implement binary search in JavaScript

问题描述

https：// www。 khanacademy.org/computing/computer-science/algorithms/binary-search/p/challenge-binary-search

我正在遵循伪代码来实现链接上的算法，但不知道我的代码有什么问题。

这是我的代码：

  / *返回数组中位置的索引，
或-1如果数组不包含targetValue * / 
 
 var doSearch = function（array，targetValue）{
 var min = 0; 
 var max = array.length  -  1; 
 var guess; 
 
 while（min< max）{
 guess =（max + min）/ 2; 
 
 if（array [guess] === targetValue）{
 return guess; 
} 
 else if（array [guess]< targetValue）{
 min = guess + 1; 
} 
 else {
 max = guess  -  1; 
} 
 
} 
 
返回-1; 
}; 
 
 var primes = [2,3,5,7,11,13,17,19,23,29,31,37，
 41,43,47,53,59， 61,67,71,73,79,83,89,97]; 
 
 var result = doSearch（primes，2）; 
 println（在索引处找到素数+结果）; 
 
 //Program.assertEqual(doSearch(primes,73），20）; 
  

解决方案

要从数组中获取值，您需要指定像 array [1] 这样的整数。 array [1.25] 将在您的情况下返回 undefined 。

<为了让它正常工作，我只需在你的循环中添加 Math.floor ，以确保我们得到一个整数。

编辑：作为@KarelG pointet，您还需要在while循环中添加< = 。这适用于 min 和 max 已变为相同的情况，在这种情况下 guess = == max === min 。如果没有< = ，循环将无法在这些情况下运行，函数将返回 -1 。

  function（array，targetValue）{
 var min = 0; 
 var max = array.length  -  1; 
 var guess; 
 
 while（min< = max）{
 guess = Math.floor（（max + min）/ 2）; 
 
 if（array [guess] === targetValue）{
 return guess; 
} 
 else if（array [guess]< targetValue）{
 min = guess + 1; 
} 
 else {
 max = guess  -  1; 
} 
 
} 
 
返回-1; 
} 
  

您可以使用 Math.floor ， Math.ceil ， Math.round 。

我希望这是一个很小的帮助，我不是很擅长解释，但我会做的就是详细说明。

https://www.khanacademy.org/computing/computer-science/algorithms/binary-search/p/challenge-binary-search

I was following the pseudo code to implement algorithm on the link but don't know what's wrong with my code.

Here is my code :

/* Returns either the index of the location in the array,
  or -1 if the array did not contain the targetValue */

    var doSearch = function(array, targetValue) {
    var min = 0;
    var max = array.length - 1;
    var guess;

    while(min < max) {
        guess = (max + min) / 2;

        if (array[guess] === targetValue) {
            return guess;
        }
        else if (array[guess] < targetValue) {
            min = guess + 1;
        }
        else {
            max = guess - 1;
        }

    }

    return -1;
};

var primes = [2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 
        41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97];

var result = doSearch(primes, 2);
println("Found prime at index " + result);

//Program.assertEqual(doSearch(primes, 73), 20);

解决方案

To get a value from an array you need to specify a whole number like array[1]. array[1.25] will return undefined in your case.

To get it working I simply added Math.floor inside you loop to insure we get a whole number.

EDIT: As @KarelG pointet out you also need to add <= in your while loop. This is for situations where min and max have become the same, in which case guess === max === min. Without the <= the loop would not run in these situations and the function would return -1.

function (array, targetValue) {
    var min = 0;
    var max = array.length - 1;
    var guess;

    while(min <= max) {
        guess = Math.floor((max + min) / 2);

        if (array[guess] === targetValue) {
            return guess;
        }
        else if (array[guess] < targetValue) {
            min = guess + 1;
        }
        else {
            max = guess - 1;
        }

    }

    return -1;
}

You could use either of Math.floor, Math.ceil, and Math.round.

I hope this was a small help, I am not very good at explaining, but I'll do my be to elaborate.

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