find-peak-element.py

Author: Chris Wu

problems/find-peak-element.py

@@ -0,0 +1,31 @@
+"""
+Take a look at the code first.
+If `nums[p]<nums[p+1]`, it means the `p` and `p+1` is at the left side of the mountain,
+We move `l` to `p+1`, since the peak must be at `p+1` or the right of the `p+1`.
+Else, it means the `p` and `p+1` is at the right side of the mountain,
+We move the `r` to `p`, since the peak must be at `p` or the left of the `p`.
+The `l` and `r` will move closer and closer to the peak until they meet together.
+The time complexity is O(LogN)
+"""
+class Solution(object):
+    def findPeakElement(self, nums):
+        l = 0
+        r = len(nums)-1
+        while l<r:
+            p = (l+r)/2
+            if nums[p]<nums[p+1]:
+                l = p+1
+            else:
+                r = p
+        return l
+
+
+#O(N) Solution
+class Solution(object):
+    def findPeakElement(self, nums):
+        if nums is None or len(nums)==0: return None
+        for i in xrange(len(nums)):
+            l = nums[i-1] if (i-1)>=0 else float('-inf')
+            r = nums[i+1] if (i+1)<len(nums) else float('-inf')
+            if nums[i]>l and nums[i]>r: return i
+        return None