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A sequence of numbers is called a wiggle sequence if the differences between successive numbers strictly alternate between positive and negative. The first difference (if one exists) may be either positive or negative. A sequence with fewer than two elements is trivially a wiggle sequence.
For example, [1,7,4,9,2,5] is a wiggle sequence because the differences (6,-3,5,-7,3) are alternately positive and negative. In contrast,[1,4,7,2,5] and [1,7,4,5,5] are not wiggle sequences, the first because its first two differences are positive and the second because its last difference is zero.
Given a sequence of integers, return the length of the longest subsequence that is a wiggle sequence. A subsequence is obtained by deleting some number of elements (eventually, also zero) from the original sequence, leaving the remaining elements in their original order.
Examples:
Input: [1,7,4,9,2,5] Output: 6 The entire sequence is a wiggle sequence. Input: [1,17,5,10,13,15,10,5,16,8] Output: 7 There are several subsequences that achieve this length. One is [1,17,10,13,10,16,8]. Input: [1,2,3,4,5,6,7,8,9] Output: 2
Follow up:
Can you do it in O(n) time?
思路：DP和贪心。
代码：
1 class Solution { 2 public: 3 int wiggleMaxLength(vector<int>& nums) { 4 int n=nums.size(); 5 if(n<2) return n; 6 int i,pre=nums[0],res=1; 7 bool increasing=nums[0]<nums[1]; 8 for(i=1;i<n;i++){ 9 if(increasing&&pre<nums[i]){ 10 increasing=!increasing; 11 res++; 12 } 13 else{ 14 if(!increasing&&pre>nums[i]){ 15 increasing=!increasing; 16 res++; 17 } 18 } 19 pre=nums[i]; 20 } 21 return res; 22 } 23 };
Leetcode 376. Wiggle Subsequence
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原文地址：http://www.cnblogs.com/Deribs4/p/5746347.html
