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Question

这是我在javascript中写二分查找代码时得到的语句。我没有t know what如果有人能解决这个错误。

        var doSearch = function(array, targetValue) {
        var min = 0;
    var max = array.length - 1;
    var guess;
    while(min <= max)
    {
        guess = Math.floor((min+max)/2);
        if(array[guess] === targetValue)
        {
        return guess;
        }
        else if(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(素数, 73), 20); // 我在这一行出错，我不知道是怎么回事，因为索引 20 是 return 并且与 20 相比，但它仍然很糟糕！

Answer 1

您需要检查值，而不是对照 targetValue

的索引

} else if (array[guess] < targetValue) {
//         ^^^^^^^^^^^^

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

    while (min <= max) {
        guess = Math.floor((min + max) / 2);
        if (array[guess] === targetValue) {
            return guess;
        }
        // no need for else, because return terminates the function
        if (array[guess] < targetValue) { // use the item, not the index
            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
];

console.log(doSearch(primes, 73));

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