递增和递减变量，直到语句为真[关闭]

Question

所以我有一个变量，范围内的值，没有办法确定确切的数字，只有一个接近它的数字（大约50以上或以下未知的数字）。假设正确的数字是910（同样，这个数字大于或小于已经确定的数字），我计算900。我如何编写一个函数来尝试900, 899, 901, 898, 902, 897...等等，直到它等于未知变量？

Answer 1

因为“未知”号码的测试实际上是一个服务器调用，所以不能用简单的循环来完成。相反，您需要异步处理所有事情。

这里有一个例子：

// Starting with guess, test that value and nearby integers up through
// guess+maxDelta and down through guess-maxDelta.
// Each number is tested by calling testMagicNumber(). This function
// can make an Ajax call or other asynchronous action, and then it
// should call the callback passed to it with true or false.
// When a match is found, call the callback function with that value.
// If no match is found call the callback function with false.
function findMagicNumber( guess, maxDelta, callback ) {
    var delta = 0, sign = +1;
    nextNumber();
    function nextNumber() {
        var value = guess + sign*delta;
        //console.log( 'Testing', value );
        testMagicNumber( value, function( match ) {
            if( match ) {
                callback( value );
            }
            else {
                if( sign > 0)
                    ++delta;
                sign = -sign;
                if( delta <= maxDelta )
                    nextNumber();
                else
                    callback( false );
            }
        });
    }
}

// Test version of a magic number matcher, using a hard coded value
function testMagicNumber( value, callback ) {
    callback( value == magic );
}

// Untested example of a function to test a magic number
// with a server request. isMagic(result) is whatever test
// you need to make on the result to get a boolean value
// for the callback.
function testMagicNumberAjax( value, callback ) {
    $.ajax({
        url: 'test',
        data: { value: value },
        error: function() {
            callback( false );
        },
        success: function( result ) {
            callback( isMagic(result) );
        }
    });
}

for( var magic = 45;  magic <= 55;  ++magic ) {
    console.log( 'Magic number is', magic );
    findMagicNumber( 50, 3, function( result ) {
        console.log( 'Matched', result );
    });
}

这需要猜测50，最大增量上下为3，并测试45到55之间的幻数。

记录的结果是：

Magic number is 45
Matched false
Magic number is 46
Matched false
Magic number is 47
Matched 47
Magic number is 48
Matched 48
Magic number is 49
Matched 49
Magic number is 50
Matched 50
Magic number is 51
Matched 51
Magic number is 52
Matched 52
Magic number is 53
Matched 53
Magic number is 54
Matched false
Magic number is 55
Matched false

testMagicNumber（）函数是进行Ajax调用以命中服务器的地方。当您从调用中得到响应时，testMagicNumber（）应该用true或false调用它的回调函数参数来指示数字是否匹配。在上面的testMagicNumberAjax（）中有一个示例（未经测试的）Ajax版本。

您可以将上面的代码粘贴到Chrome控制台中进行快速测试；更改magic的值以尝试不同的数字。

Answer 2

var guess = x;
var answer = 910;
var high = guess;
var low = guess;

while (high !== answer && low !== answer) {
    high++;
    low--;
}

if (high === answer) {
    print high;
} else if (low === answer) {
    print low;
} else {
    print "how did you get here?";
}