常见的查找算法----折半查找（JavaScript实现）

递归实现

    function binarySearch (arr, element) {
        return searchSort(arr, element, 0, arr.length-1);
    }
    function searchSort(arr, element, left, right) {
        if(left > right) {
            return -1;
        }
        var mid = Math.floor((left + right) / 2);
        if(arr[mid] == element) {
            return mid;
        }else if(arr[mid] > arr[left]) {
            right = mid - 1;
        } else {
            left = mid + 1;
        }
        return searchSort(arr, element, left, right);
    }

    var arr = [17,31,45,80,67,45,56,79];
    console.log(binarySearch(arr, 100));

非递归实现

function binarySearch (arr, element) {
    if(!arr) {
        return -1；
    }
    var left = 0;
    var right = arr.length - 1;
    var mid;
    while(left <= right) {
        mid = Math.floor((left+right)/2);
        if(arr[mid] == element) {
            return mid;
        } else if(arr[mid] > element) {
            right = mid - 1;
        } else {
            left = mid + 1;
        }
    }
    return -1;
}
var arr = [17,31,45,80,67,45,56,79];
console.log(binarySearch(arr, 100));