Algorithm
Problem Name: 376. Wiggle Subsequence
A wiggle sequence is a sequence where 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 one element and a sequence with two non-equal elements are trivially wiggle sequences.
- For example,
[1, 7, 4, 9, 2, 5]is a wiggle sequence because the differences(6, -3, 5, -7, 3)alternate between positive and negative. - In contrast,
[1, 4, 7, 2, 5]and[1, 7, 4, 5, 5]are not wiggle sequences. The first is not because its first two differences are positive, and the second is not because its last difference is zero.
A subsequence is obtained by deleting some elements (possibly zero) from the original sequence, leaving the remaining elements in their original order.
Given an integer array nums, return the length of the longest wiggle subsequence of nums.
Example 1:
Input: nums = [1,7,4,9,2,5] Output: 6 Explanation: The entire sequence is a wiggle sequence with differences (6, -3, 5, -7, 3).
Example 2:
Input: nums = [1,17,5,10,13,15,10,5,16,8] Output: 7 Explanation: There are several subsequences that achieve this length. One is [1, 17, 10, 13, 10, 16, 8] with differences (16, -7, 3, -3, 6, -8).
Example 3:
Input: nums = [1,2,3,4,5,6,7,8,9] Output: 2
Constraints:
1 <= nums.length <= 10000 <= nums[i] <= 1000
Code Examples
#1 Code Example with Java Programming
Code -
Java Programming
class Solution {
public int wiggleMaxLength(int[] nums) {
if (nums.length < 2) {
return nums.length;
}
int[] increasing = new int[nums.length];
int[] decreasing = new int[nums.length];
for (int i = 0; i < nums.length; i++) {
for (int j = 0; j < i; j++) {
if (nums[i] > nums[j]) {
increasing[i] = Math.max(increasing[i], decreasing[j] + 1);
} else if (nums[i] < nums[j]) {
decreasing[i] = Math.max(decreasing[i], increasing[j] + 1);
}
}
}
return 1 + Math.max(decreasing[nums.length - 1], increasing[nums.length - 1]);
}
}
Input
Output
#2 Code Example with Javascript Programming
Code -
Javascript Programming
const wiggleMaxLength = function(nums) {
if (nums.length < 2) return nums.length
let prevdiff = nums[1] - nums[0]
let count = prevdiff !== 0 ? 2 : 1
for (let i = 2; i < nums.length; i++) {
let diff = nums[i] - nums[i - 1]
if ((diff > 0 && prevdiff <= 0) || (diff < 0 && prevdiff >= 0)) {
count++
prevdiff = diff
}
}
return count
}
Input
Output
#3 Code Example with Python Programming
Code -
Python Programming
class Solution:
def wiggleMaxLength(self, nums):
if len(nums) <= 2: return 0 if not nums else 1 if nums[0] == nums[-1] else 2
inc = nums[0] < nums[1] if nums[0] != nums[1] else None
cnt = 2 if inc != None else 1
for i in range(2, len(nums)):
if nums[i - 1] != nums[i] and (inc == None or inc != (nums[i - 1] < nums[i])):
inc = nums[i - 1] < nums[i]
cnt += 1
return cnt
Input
Output