二分搜索首次出现被搜索元素的位置

在一个已经排序的非降序整形数组中，找到被搜索整数首次出现的位置，如果该整数出现多次的话。要求在log₂n次比交内完成。

 

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace ConsoleApplication3
{
    class Program
    {
        static void Main(string[] args)
        {
            int[] a = new int[] { 1, 1, 1, 1, 2, 2, 2, 2, 2, 3, 3, 3, 3, 4, 4, 4, 5, 6, 7, 7, 7, 7, 7 };

            for (int i = 1; i <= 7; ++i)
            {
                Console.WriteLine(string.Format("Search {0}, Index: {1}, TestResult: {2}",
                    i, 
                    biSearch(a, i),
                    biSearch(a, i) == sequenceSearch(a, i)));
            }
        }

        static int biSearch(int[] a, int t)
        {
            int n = a.Length;
            int l = 0; int b = n - 1;
            int f = -1;
            int m = -1;
            while (l <= b)
            {
                m = (l + b) / 2;

                if (a[m] < t)
                {
                    l = m + 1;
                }

                else if (a[m] == t)
                {
                    f = m;
                    b = m - 1;
                }
                else //a[m] > t
                {
                    b = m - 1;
                }
            }

            return f;
        }

        static int sequenceSearch(int[] a, int t)
        {
            for (int i = 0; i<a.Length; ++i)
            {
                if (t == a[i]) return i;
            }

            return -1;
        }
    }
}