khan-academy - 可汗学院二分搜索算法第 3 步正确，但未通过。

Question

我正在处理 Khan Academy Binary Search problem第三步是要求对“...帮助可视化搜索需要多长时间”进行一些基本的补充。

提示要求“...添加一个 println() 语句，该语句显示查找结果所需的猜测总数。 您的函数应该只在找到目标时打印猜测的总数。你的函数不应该打印每个循环的猜测次数。”

我已经使用递增计数器和带有该变量的 println() 成功完成了这项工作。运行代码可以完美运行，但是可汗学院预建环境不会让我通过这一步。他们还有其他期待的方式吗？

代码在这里:

/* 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;
    var guessTotal = 0;

    while(min <= max){
        guess = Math.floor((min + max) / 2);
        println("You guessed " + guess);
        if(array[guess] === targetValue){
            println(guessTotal);
            return guess;
        }
        else if (array[guess] < targetValue){
            min = guess + 1;
        }
        else{
            max = guess -1;
        }
        guessTotal ++;
    }
    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, 73);
println("Found prime at index " + result);

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

注意:我还尝试使用 guess 和 guessTotal 添加返回数组，然后从 result 打印它们。这也符合他们的要求，但也没有通过。

Answer 1

正确答案

 /* 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;
    var guessTotal = 0;
     while(min <= max) {
        guess = Math.floor((max + min) / 2);
        println(guess);
        guessTotal++;
        if (array[guess] === targetValue) {
            println(guessTotal);
            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, 73);
println("Found prime at index " + result);

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