Wiggle Subsequence
leetcode 376. Wiggle Subsequence
Top-down DP
TIP
up as the largest wiggle subsequence that the last number increases. such as 1,3,2,5.
down share similar thoughts.
cpp
class Solution {
public:
int wiggleMaxLength(vector<int>& nums) {
int s = nums.size();
if(s == 0) return 0;
vector<int>up(s,0);
vector<int>down(s,0);
up[0] = 1; down[0] = 1;
for(int i = 1; i < s; i++){
if(nums[i] < nums[i-1]){
down[i] = up[i-1]+1;
up[i] = up[i-1];
}
else if(nums[i] > nums[i-1]){
down[i] = down[i-1];
up[i] = down[i-1]+1;
}
else{
down[i] = down[i-1];
up[i] = up[i-1];
}
}
return max(up[s-1],down[s-1]);
}
};Optimization
WARNING
Already 0ms for its runtime, but still can optimize it memory to O(1).
cpp
class Solution {
public:
int wiggleMaxLength(vector<int>& nums) {
int s = nums.size();
if(s == 0) return 0;
int up = 1, down = 1;
for(int i = 1; i < s; i++){
if(nums[i] < nums[i-1]){
down = up + 1;
}
else if(nums[i] > nums[i-1]){
up = down + 1;
}
}
return max(up,down);
}
};