我们把符合下列属性的数组 A 称作山脉:
A.length >= 3
存在 0 < i < A.length - 1 使得A[0] < A[1] < … A[i-1] < A[i] > A[i+1] > … > A[A.length - 1]
给定一个确定为山脉的数组,返回任何满足 A[0] < A[1] < … A[i-1] < A[i] > A[i+1] > … > A[A.length - 1] 的 i 的值。
示例 1:
输入:[0,1,0]
输出:1
示例 2:
输入:[0,2,1,0]
输出:1
提示:
3 <= A.length <= 10000
0 <= A[i] <= 10^6
A 是如上定义的山脉
简单的Python:
class Solution:
def peakIndexInMountainArray(self, A: List[int]) -> int:
return A.index(max(A))
其余的二分查找:
一般存在三种情况:
1、A[mid+1]>A[mid]>A[mid-1];
2、A[mid+1]<A[mid]<A[mid-1];
3、就是索要找的山峰情况;
class Solution {
public:
int peakIndexInMountainArray(vector<int>& A) {
int len = A.size();
int high = len-1, low = 0;
int mid;
while(low<=high){
mid = (low + high)/2;
// cout<<mid<<endl;
if(A[mid-1]<A[mid]&&A[mid]<A[mid+1]){
low = mid + 1;
// cout<<low<<endl;
}else if(A[mid-1]>A[mid]&&A[mid]>A[mid+1]){
high = mid - 1;
cout<<high<<endl;
}else{
// cout<<mid<<endl;
return mid;
}
}
return mid;
}
};