二分查找

1.递归实现

function binarySearch(data, dest, start, end){
    var end = end || data.length - 1,
        start = start || 0,
        m = Math.floor((start + end) / 2);
    if(data[m] == dest){
        return m;
    }
    if(dest < data[m]){
        return binarySearch(data, dest, 0, m-1);
    }else{
        return binarySearch(data, dest, m+1, end);
    }
  
    return false;
}
var arr = [-34, 1, 3, 4, 5, 8, 34, 45, 65, 87];
binarySearch(arr,4);
//3

2.非递归实现

function binarySearch(data, dest){
    var h = data.length - 1,
        l = 0;
    while(l <= h){
        var m = Math.floor((h + l) / 2);
        if(data[m] == dest){
            return m;
        }
        if(dest > data[m]){
            l = m + 1;
        }else{
            h = m - 1;
        }
    }
  
    return false;
}
var arr = [-34, 1, 3, 4, 5, 8, 34, 45, 65, 87];
binarySearch(arr,4);
//3