二分查找

 public int search()
        {
            int key = 2;
            int[] a = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };
            int low = 0;
            int high = a.Length - 1;Stack st = new Stack();
            while (low <= high)
            {
                int mid = low + (high - low) / 2;
                if (a[mid] > key)
                {
                    high = mid - 1;
                }
                else if (a[mid] < key)
                {
                    low = mid + 1;
                }
                else
                {
                    return mid;
                }
            }
            return -1;
        }

%% erlang实现的列表二分查找,erlang:length,erlang:nth等函数都可以用遍历实现,这里为了方便直接采用
binary_search(Key, List) ->
    High = erlang:length(List),
    Low = 1,
    do_binary_search(Low, High, Key, List).

do_binary_search(Low, High, _Key, _List) when Low > High -> %% 查找不到,返回-1
    -1;
do_binary_search(Low, High, Key, List) ->
    Mid = Low + (High - Low) div 2, %% 求出中间键
    Value = lists:nth(Mid, List), %% 获取中间键的值,尾递归遍历获取,性能消耗
    if Key > Value -> %% 大于中间键的值,去后半部分查找
        do_binary_search(Mid + 1, High, Key, List);
       Key < Value -> %% 小于中间键的值,去前半部分查找
        do_binary_search(Low, Mid - 1, Key, List);
       true -> %% 直接返回查找的键
           Mid
    end.
%%注意：传入的List是列表 ，因为lists:nth的遍历有较大的性能消耗；

binary_search_tuple(Key, List) ->
    Tuple = erlang:list_to_tuple(List),
    High = erlang:tuple_size(Tuple),
    Low = 1,
    do_binary_search_tuple(Low, High, Key, Tuple).

do_binary_search_tuple(Low, High, _Key, _Tuple) when Low > High ->
    -1;
do_binary_search_tuple(Low, High, Key, Tuple) ->
    Mid = Low + (High - Low) div 2,
    Value = erlang:element(Mid, Tuple),
    if Key > Value ->
        do_binary_search_tuple(Mid + 1, High, Key, Tuple);
        Key < Value ->
            do_binary_search_tuple(Low, Mid - 1, Key, Tuple);
        true ->
            Mid
    end.