/// <summary>
/// 查找峰顶索引
/// </summary>
/// <param name="mountainArr"></param>
/// <returns></returns>
private int PeakIndexInMountainArray(MountainArray A)
{
int left = 0, right = A.Length() - 1;
int mid = 0;
while (left <= right)
{
mid = left + ((right - left) >> 1);
if (mid == 0)
{
if (A.Get(mid) < A.Get(mid + 1))
{
return(mid + 1);
}
else
{
return(mid);
}
}
else if (mid == A.Length() - 1)
{
if (A.Get(mid - 1) > A.Get(mid))
{
return(mid - 1);
}
else
{
return(mid);
}
}
else if (A.Get(mid - 1) < A.Get(mid) && A.Get(mid) < A.Get(mid + 1))
{
left = mid + 1;
}
else if (A.Get(mid - 1) > A.Get(mid) && A.Get(mid) > A.Get(mid + 1))
{
right = mid - 1;
}
else
{
return(mid);
}
}
return(-1);
}
/// <summary>
/// 1095. 山脉数组中查找目标值
/// </summary>
/// <param name="target"></param>
/// <param name="mountainArr"></param>
/// <returns></returns>
public int FindInMountainArray(int target, MountainArray mountainArr)
{
int peakIndex = PeakIndexInMountainArray(mountainArr);
if (target > mountainArr.Get(peakIndex))
{
return(-1);
}
int minLeft = BinarySearchLeft(target, peakIndex, mountainArr);
if (minLeft != -1)
{
return(minLeft);
}
int minRight = BinarySearchRight(target, peakIndex + 1, mountainArr);
return(minRight);
}
private int BinarySearchRight(int target, int low, MountainArray mountainArr)
{
int left = low, right = mountainArr.Length() - 1, mid = 0;
int min = -1;
while (left <= right)
{
mid = left + ((right - left) >> 1);
if (mountainArr.Get(mid) < target)
{
right = mid - 1;
}
else if (mountainArr.Get(mid) > target)
{
left = mid + 1;
}
else
{
min = mid;
right = mid - 1;
}
}
return(min);
}
