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【LeetCode】Find Peak Element (3 solutions)
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.
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.
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Note:
Your solution should be in logarithmic complexity.
这题就是求序列最大值。顺序查找或二分查找均可。
满足复杂度要求的话需要用二分查找。
解法一：顺序查找
class Solution {public: int findPeakElement(const vector<int> &num) { for(int i = 1; i < num.size(); i ++) { if(num[i] < num[i-1]) {// < return i-1; } } return num.size()-1; }};
解法二：二分查找（递归）
class Solution {public: int findPeakElement(const vector<int> &num) { return Helper(num, 0, num.size()-1); } int Helper(const vector<int> &num, int low, int high) { if(low == high) return low; else { int mid1 = (low+high)/2; int mid2 = mid1+1; if(num[mid1] > num[mid2]) return Helper(num, low, mid1); else return Helper(num, mid2, high); } }};
解法三：二分查找（迭代）
class Solution {public: int findPeakElement(const vector<int> &num) { int low = 0; int high = num.size()-1; while(low < high) { int mid1 = (low+high)/2; int mid2 = mid1+1; if(num[mid1] < num[mid2]) low = mid2; else high = mid1; } return low; }};
【LeetCode】Find Peak Element (3 solutions)
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