讀處

【原題目】:

Let's call an array A a mountain if the following properties hold:

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

Given an array that is definitely a mountain,

return any i such that A[0] < A[1] < ... A[i-1] < A[i] > A[i+1] > ... > A[A.length - 1].

Example 1:

Input: [0,1,0]
Output: 1

Input: [0,2,1,0]
Output: 1

Note:

1. 3 <= A.length <= 10000
2. 0 <= A[i] <= 10^6
3. A is a mountain, as defined above.

參考 : https://leetcode.com/problems/peak-index-in-a-mountain-array/

【My Solution1】: 線性解法，時間複雜度 : O(n)

【My Solution2】: Binary Search 二元搜尋法 時間複雜度 : O(nlogn)

如果左邊的比中間大，就往左邊找

如果右邊的比中間大，就往右邊找