数组局部峰值(二分搜索, 注意边界确定)

Author: cls1991

BinarySearch/162_FindPeakElement.py

@@ -0,0 +1,44 @@
+# coding: utf8
+
+
+"""
+    题目链接: https://leetcode.com/problems/find-peak-element/description.
+    题目描述:
+
+    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.
+
+    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[n] = -∞.
+
+    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.
+
+    Note:
+    Your solution should be in logarithmic complexity.
+
+    Credits:
+    Special thanks to @ts for adding this problem and creating all test cases.
+
+"""
+
+
+class Solution(object):
+    def findPeakElement(self, nums):
+        """
+        :type nums: List[int]
+        :rtype: int
+        """
+        left, right = 0, len(nums) - 1
+        # 局部峰值落在哪个半区
+        while left < right:
+            mid = left + (right - left) // 2
+            if nums[mid] < nums[mid + 1]:
+                left = mid + 1
+            else:
+                right = mid
+
+        return right

README.md

@@ -3,13 +3,14 @@ leetcode刷题, 直接用leetcode的分类方式.
 
 - [x] 数组 (完成时间: 2018-01-23)
 -  字符串
--  链表
+- [x] 链表 (完成时间: 2018-01-28) 
 -  哈希表
 -  堆栈
 -  双指针
--  树
+- [x] 树 (完成时间: 2018-02-04)
 -  图
 -  深搜/广搜
+- [x] 二分搜索 (完成时间: 2018-02-06)
 -  动规
 -  其他: 数学, 位操作, 设计题等