Today I have done leetcode's October LeetCoding Challenge with cpp.

October LeetCoding Challenge 12

Description

Find in Mountain Array

(This problem is an interactive problem.)

You may recall that an array arr is a mountain array if and only if:

• arr.length >= 3
• There exists some i with 0 < i < arr.length - 1 such that:
  • arr[0] < arr[1] < ... < arr[i - 1] < arr[i]
  • arr[i] > arr[i + 1] > ... > arr[arr.length - 1]

Given a mountain array mountainArr, return the minimum index such that mountainArr.get(index) == target. If such an index does not exist, return -1.

You cannot access the mountain array directly. You may only access the array using a MountainArray interface:

• MountainArray.get(k) returns the element of the array at index k (0-indexed).
• MountainArray.length() returns the length of the array.

Submissions making more than 100 calls to MountainArray.get will be judged Wrong Answer. Also, any solutions that attempt to circumvent the judge will result in disqualification.

Example 1:

Input: array = [1,2,3,4,5,3,1], target = 3
Output: 2
Explanation: 3 exists in the array, at index=2 and index=5. Return the minimum index, which is 2.

Example 2:

Input: array = [0,1,2,4,2,1], target = 3
Output: -1
Explanation: 3 does not exist in the array, so we return -1.

Constraints:

• 3 <= mountain_arr.length() <= 104
• 0 <= target <= 109
• 0 <= mountain_arr.get(index) <= 109

Solution

class Arr {
  MountainArray &mountainArr;
  map<int, int> arr;
  public:
  Arr(MountainArray &m): mountainArr(m) {}

  int &operator[](int index) {
    if(arr.count(index)) return arr[index];
    arr[index] = mountainArr.get(index);
    return arr[index];
  }
};

class Solution {
public:
  int findInMountainArray(int target, MountainArray &mountainArr) {
    Arr a(mountainArr);
    int len = mountainArr.length();
    int low = 1;
    int high = len - 2;
    int peak;
    while(low <= high) {
      int mid = (low + high) / 2;
      if(a[mid] > a[mid - 1] && a[mid] > a[mid + 1]) {
        peak = mid;
        break;
      } else if(a[mid] > a[mid - 1]) {
        low = mid + 1;
      } else {
        high = mid - 1;
      }
    }

    low = 0;
    high = peak;
    while(low < high) {
      int mid = (low + high) / 2;
      if(a[mid] < target) {
        low = mid + 1;
      } else {
        high = mid;
      }
    }
    cout << low << ' ' << high << endl;
    if(a[low] == target) return low;
    low = peak;
    high = len - 1;
    while(low < high) {
      int mid = (low + high) / 2;
      if(a[mid] > target) {
        low = mid + 1;
      } else {
        high = mid;
      }
    }
    if(a[low] == target) return low;
    return -1;
  }
};

// Accepted
// 79/79 cases passed (0 ms)
// Your runtime beats 100 % of cpp submissions
// Your memory usage beats 14.97 % of cpp submissions (7.5 MB)