[LeetCode] Find Peak Element

Find Peak Element

A peak element is an element that is greater than its neighbors.

Given an input array where num[i] ≠ num[i+1], find a peak element and return its index.

The array may contain multiple peaks, in that case return the index to any one of the peaks is fine.

You may imagine that num[-1] = num[n] = -∞.

For example, in array [1, 2, 3, 1], 3 is a peak element and your function should return the index number 2.

解題思路：

這道題挺簡單的，只要返回其中一個峰值即可。只需最多掃描一次數組。官方說二分法，我認為是一樣的效率的，因為這個數組是隨機排列的嘛。注意特殊情況的處理。

class Solution {
public:
    int findPeakElement(const vector &num) {
        int len=num.size();
        //處理特殊情況
        if(len==0||len==1){
            return 0;
        }
        if(num[0]>num[1]){
            return 0;
        }
        if(num[len-1]>num[len-2]){
            return len-1;
        }
        for(int i=1; inum[i-1]&&num[i]>num[i+1]){
                return i;
            }
        }
        return 0;
    }
};