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1095. Find in Mountain Array 👍

  • Time: $O(\log n)$
  • Space: $O(1)$
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/**
 * // This is the MountainArray's API interface.
 * // You should not implement it, or speculate about its implementation
 * class MountainArray {
 *  public:
 *   int get(int index);
 *   int length();
 * };
 */

class Solution {
 public:
  int findInMountainArray(int target, MountainArray& mountainArr) {
    const int n = mountainArr.length();
    const int peakIndex = peakIndexInMountainArray(mountainArr, 0, n - 1);

    const int leftIndex = searchLeft(mountainArr, target, 0, peakIndex);
    if (mountainArr.get(leftIndex) == target)
      return leftIndex;

    const int rightIndex =
        searchRight(mountainArr, target, peakIndex + 1, n - 1);
    if (mountainArr.get(rightIndex) == target)
      return rightIndex;

    return -1;
  }

 private:
  // 852. Peak Index in a Mountain Array
  int peakIndexInMountainArray(MountainArray& A, int l, int r) {
    while (l < r) {
      const int m = (l + r) / 2;
      if (A.get(m) < A.get(m + 1))
        l = m + 1;
      else
        r = m;
    }
    return l;
  }

  int searchLeft(MountainArray& A, int target, int l, int r) {
    while (l < r) {
      const int m = (l + r) / 2;
      if (A.get(m) < target)
        l = m + 1;
      else
        r = m;
    }
    return l;
  }

  int searchRight(MountainArray& A, int target, int l, int r) {
    while (l < r) {
      const int m = (l + r) / 2;
      if (A.get(m) > target)
        l = m + 1;
      else
        r = m;
    }
    return l;
  }
};
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/**
 * // This is MountainArray's API interface.
 * // You should not implement it, or speculate about its implementation
 * interface MountainArray {
 *   public int get(int index) {}
 *   public int length() {}
 * }
 */

class Solution {
  public int findInMountainArray(int target, MountainArray mountainArr) {
    final int n = mountainArr.length();
    final int peakIndex = peakIndexInMountainArray(mountainArr, 0, n - 1);

    final int leftIndex = searchLeft(mountainArr, target, 0, peakIndex);
    if (mountainArr.get(leftIndex) == target)
      return leftIndex;

    final int rightIndex = searchRight(mountainArr, target, peakIndex + 1, n - 1);
    if (mountainArr.get(rightIndex) == target)
      return rightIndex;

    return -1;
  }

  // 852. Peak Index in a Mountain Array
  private int peakIndexInMountainArray(MountainArray A, int l, int r) {
    while (l < r) {
      final int m = (l + r) / 2;
      if (A.get(m) < A.get(m + 1))
        l = m + 1;
      else
        r = m;
    }
    return l;
  }

  private int searchLeft(MountainArray A, int target, int l, int r) {
    while (l < r) {
      final int m = (l + r) / 2;
      if (A.get(m) < target)
        l = m + 1;
      else
        r = m;
    }
    return l;
  }

  private int searchRight(MountainArray A, int target, int l, int r) {
    while (l < r) {
      final int m = (l + r) / 2;
      if (A.get(m) > target)
        l = m + 1;
      else
        r = m;
    }
    return l;
  }
}
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# """
# This is MountainArray's API interface.
# You should not implement it, or speculate about its implementation
# """
# class MountainArray:
#   def get(self, index: int) -> int:
#   def length(self) -> int:

class Solution:
  def findInMountainArray(self, target: int, mountain_arr: 'MountainArray') -> int:
    n = mountain_arr.length()
    peakIndex = self.peakIndexInMountainArray(mountain_arr, 0, n - 1)

    leftIndex = self.searchLeft(mountain_arr, target, 0, peakIndex)
    if mountain_arr.get(leftIndex) == target:
      return leftIndex

    rightIndex = self.searchRight(mountain_arr, target, peakIndex + 1, n - 1)
    if mountain_arr.get(rightIndex) == target:
      return rightIndex

    return -1

  # 852. Peak Index in a Mountain Array
  def peakIndexInMountainArray(self, A: 'MountainArray', l: int, r: int) -> int:
    while l < r:
      m = (l + r) // 2
      if A.get(m) < A.get(m + 1):
        l = m + 1
      else:
        r = m
    return l

  def searchLeft(self, A: 'MountainArray', target: int, l: int, r: int) -> int:
    while l < r:
      m = (l + r) // 2
      if A.get(m) < target:
        l = m + 1
      else:
        r = m
    return l

  def searchRight(self, A: 'MountainArray', target: int, l: int, r: int) -> int:
    while l < r:
      m = (l + r) // 2
      if A.get(m) > target:
        l = m + 1
      else:
        r = m
    return l