Editing 二分算法示例，针对按顺序排好的索引数组

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    <title>二分算法示例，针对按顺序排好的索引数组</title>
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var binarySearch = function (arr, start, stop, num) {
    if (stop - start == 1) {
        if (arr[start] == num) {
            return start;
        }
        if (arr[stop] == num) {
            return stop;
        }
        return -1;
    }
    var center = Math.floor((start + stop) / 2);
    if (num != arr[center]) {
        return num > arr[center] ? binarySearch(arr, center, stop, num)
            : binarySearch(arr, start, center, num);
    }
    return center;
}

var arr = [1, 4, 6, 12, 15, 20, 38, 44];
console.log(arr)
console.log('find 2 : ' + binarySearch(arr, 0, arr.length, 2));
console.log('find 38 : ' + binarySearch(arr, 0, arr.length, 38));
console.log('find 15 : ' + binarySearch(arr, 0, arr.length, 15));