peak-index-in-a-mountain-array.py

Author: Chris Wu

problems/peak-index-in-a-mountain-array.PY

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+"""
+Take a look at the code first.
+If `A[p]<A[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 peakIndexInMountainArray(self, A):
+        l = 0
+        r = len(A)-1
+        while l<r:
+            p = (l+r)/2
+            if A[p]<A[p+1]:
+                l = p+1
+            else:
+                r = p
+        return l