LeetCode 376 swing sequence

• analysis

     This question is a greedy question. If the points in the array are drawn in two-dimensional coordinates, it is a polyline. You only need to count the number of inflection points.

It should be noted that the code uses the idea of ​​automata, which is more readable than the code that only writes if else

If you write such code in an interview, you can show a solid basic skill.

• Code

class Solution {
public:
    int wiggleMaxLength(vector<int>& nums) {
        int size = nums.size();
        if(size < 2) return nums.size();

        static const int BEGIN = 0;
        static const int UP = 1;
        static const int DOWN = 2;

        int state = BEGIN;
        int max_length = 1;

        for(int i = 1; i < size; ++i ){
            switch(state){
                case BEGIN:
                    if(nums[i] > nums[i - 1]){
                        state = UP;
                        ++max_length;
                    }else if(nums[i] < nums[i - 1]){
                        state = DOWN;
                        ++max_length;
                    }
                    break;
                case UP:
                    if(nums[i - 1] > nums[i]){
                        state = DOWN;
                        ++max_length;
                    }
                    break;
                case DOWN:
                    if(nums[i - 1] < nums[i]){
                        state = UP;
                        ++max_length;
                    }
                break;
            }
        }
        return max_length;
    }
};