leetcode:Find Peak Element
2014-12-23 14:57
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A peak element is an element that is greater than its neighbors.
Given an input array where
The array may contain multiple peaks, in that case return the index to any one of the peaks is fine.
You may imagine that
For example, in array
the index number 2.
click to show spoilers.
Credits:
Special thanks to @ts for adding this problem and creating all test cases.
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 = -∞.
For example, in array
[1, 2, 3, 1], 3 is a peak element and your function should return
the index number 2.
click to show spoilers.
Credits:
Special thanks to @ts for adding this problem and creating all test cases.
class Solution { public: int findPeakElementInternal(const vector<int> &num, int startPos, int endPos) { if (startPos == endPos) return startPos; int mid = (startPos+endPos)/2; if (mid == 0 && num[1] < num[0]) return 0; if (mid == num.size()-1 && num[num.size()-2] < num[num.size()-1]) return num.size()-1; if (num[mid] > num[mid-1] && num[mid] > num[mid+1]) return mid; if (num[mid] < num[mid+1]) return findPeakElementInternal(num, mid+1, endPos); else if (num[mid] < num[mid-1]) return findPeakElementInternal(num, startPos, mid-1); } int findPeakElement(const vector<int> &num) { return findPeakElementInternal(num, 0, num.size()-1); } };
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