使用JavaScript实现二分查找

递归版

    //数组，找谁， 低位， 高位
    function BSearch( arr, x, low, high){
        if( low > high ){
            return -1;
        }
        var mid = parseInt((low + high) / 2);
        if( x == arr[mid] ){
            return mid;
        }
        else if( x < arr[mid] ){
            return BSearch(arr, x, low, mid-1);
        }
        else{
            return BSearch(arr, x, mid+1, high );
        }

    }

    var arr = [1,3,4,5,17,18,31,44];
    var f = BSearch( arr, 44, 0,arr.length-1 );
    if( f=== -1 ){
        console.log("查无此人");
    }
    else{
        console.log("下标为"+f);
    }

迭代版

function BSearch( arr, n, low, high ){
        while( low <= high ){
            var mid = parseInt( (low+high)/2 );
            if( n < arr[mid] ){
                high= mid-1;
            }
            else if( n>arr[mid] ){
                low = mid+1;
            }
            else{
                return mid;
            }
        }

        return -1;
    }

    var arr = [1,3,4,5,17,18,31,44];
    var f = BSearch( arr, 44, 0,arr.length-1 );
    if( f=== -1 ){
        console.log("查无此人");
    }
    else{
        console.log("下标为"+f);
    }