二分查找

二分查找

		// 非递归算法
        function binary_search(arr, key) {
            var low = 0,
                high = arr.length - 1;
            while(low <= high){
                var mid = parseInt((high + low) / 2);
                if(key == arr[mid]){
                    return  mid;
                }else if(key > arr[mid]){
                    low = mid + 1;
                }else if(key < arr[mid]){
                    high = mid -1;
                }else{
                    return -1;
                }
            }
        };
        var arr = [1,2,3,4,5,6,7,8,9,10,11,23,44,86];
        var result = binary_search(arr,10);
        alert(result); // 9 返回目标元素的索引值     

		// 递归算法
        function binary_search(arr,low, high, key) {
            if (low > high){
                return -1;
            }
            var mid = parseInt((high + low) / 2);
            if(arr[mid] == key){
                return mid;
            }else if (arr[mid] > key){
                high = mid - 1;
                return binary_search(arr, low, high, key);
            }else if (arr[mid] < key){
                low = mid + 1;
                return binary_search(arr, low, high, key);
            }
        };
        var arr = [1,2,3,4,5,6,7,8,9,10,11,23,44,86];
        var result = binary_search(arr, 0, 13, 10);
        alert(result); // 9 返回目标元素的索引值  

效率为 O(logn)