LeetCode刷题：852.Peak Index in a Mountain Array

852. Peak Index in a Mountain Array

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

Example 2:

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.

   解题思路：

   指定临时变量peak和peak_index，peak与A[i]进行比较，若peak小于A[i]，则令peak = A[i]; peak_index = i;，遍历数组，直到peak取到最大值，peak_index为peak取最大时的i值

   解答：

   class Solution {
   public:
   int peakIndexInMountainArray(vector<int>& A) {
       int peak = 0, peak_index = 0;
       auto len = A.size() - 1;
       for(int i = 0; i < len; ++i)
       {
           if(peak < A[i])
           {
               peak = A[i];
               peak_index = i;
           }
       }
       return peak_index;
   }
   };