新手算法学习之路----二分法Search-for-a-Range

public static int[] searchRange(int[] A, int target) {
           int start=0, end = A.length-1;
           int mid,left_position=-1,right_position=-1;
           int result[] = {left_position,right_position};
           if(A.length == 0) return result;
             while(start<end-1){
                  mid = start+(end-start)/2;
                  if(A[mid]<target){
                     start = mid +1;
                  }else if(A[mid]>target){
                     end = mid-1;
                  }else{
                   left_position=Search_Middle_left(A, start, mid-1,target);
                   right_position=Search_Middle_right(A, mid+1, end,target);
                   break;
                  }
             }
              //int []resualt={left_position,right_position};
              //return resualt;      
              return new int[]{left_position,right_position};
    }
    
     public static int Search_Middle_right(int[] A, int low, int high,int target){
         int this_low = low, this_high=high;
         int mid;
         while(this_low+1<this_high){
             mid = this_low+(this_high-this_low)/2;//在上一个中点的左边找target值，左边是不可能有元素值小于target 所以只讨论 等于 和大于的时候
             if(A[mid]==target){          //target值等于mid的时候，继续往序列的左边找，              
                this_low = mid;           //当中间值等于target时候，如果要往右继续寻找，就必须从mid的那个位置开始，如果从mid-1，那么如果从mid-1位置就大于target，那么程序就要出错了
             }else if(A[mid]>target){     //target值小于mid的时候，往mid的右边找
                this_high = mid -1;
             }
          }
         if(A[this_low]==target)
          return this_low;
         else return this_high;       
       }
    
     public static int Search_Middle_left(int[]A, int low ,int high, int target){
         int this_low = low, this_high=high;
         int mid;
         while(this_low+1<this_high){               // 当中间值等于target值的时候在左边部分找，左边部分不能有大于target的值，所以不考虑A[mid]>target的时候
             mid = this_low+(this_high-this_low)/2;
             if(A[mid]==target){            // 中间值等于target的时候继续往左找
                this_high = mid;
             }else if(A[mid]<target) {   //如果中间值小于target值的时候，就往右找
                this_low = mid +1;
             }
          }
         if(A[this_high]==target)
          return this_high;
         else return this_low;
       }