力扣1095.山脉数组中查找目标值

先二分出峰顶的下标
- 然后分为左右两段再做二分
  class Solution {
  public:
      int findInMountainArray(int target, MountainArray &mountainArr) {
          int l = 0,r = mountainArr.length()-1;
          while(l<r)
          {
              int mid = (l + r + 1) / 2;
              if(mountainArr.get(mid) > mountainArr.get(mid - 1)) l = mid;
              else r = mid - 1;
          }
          int peak = r;
          if(mountainArr.get(peak) == target) return peak;
          l = 0,r = peak;
          while(l<r)
          {
              int mid = (l + r) / 2;
              if(mountainArr.get(mid) >= target) r = mid;
              else l = mid + 1;
          }
          if(mountainArr.get(l) == target) return l;
  
          l = peak,r = mountainArr.length() - 1;
          while(l<r)
          {
              int mid = (l + r + 1) / 2;
              if(mountainArr.get(mid) >= target) l = mid;
              else r = mid - 1;
          }
          if(mountainArr.get(l) == target) return l;
          return -1;
      }
  };