[C++知识库]135. 分发糖果 C++ 2021-08-24

135. 分发糖果

class Solution {
public:
    int candy(vector<int>& ratings) 
    {
        int len = ratings.size();
        vector<int> left(len, 1);
        vector<int> right(len, 1);
        vector<int> count(len, 1);

        for (int i = 1; i < len; ++i)
        {
            if (ratings[i] > ratings[i - 1])
            {
                left[i] = left[i - 1] + 1;
            }
        }
        int sum = left[len - 1];
        for (int i = len - 2; i >= 0; --i)
        {
            if (ratings[i] > ratings[i + 1])
            {
                right[i] = right[i + 1] + 1;
            }
            sum += max(left[i], right[i]);
        }
        return sum;
    }
};

优化一点空间, 不要vector left

class Solution {
public:
    int candy(vector<int>& ratings) 
    {
        int len = ratings.size();
        vector<int> left(len, 1);
        vector<int> count(len, 1);

        for (int i = 1; i < len; ++i)
        {
            if (ratings[i] > ratings[i - 1])
            {
                left[i] = left[i - 1] + 1;
            }
        }
        
        int sum = left[len - 1];
        int right = 1;
        for (int i = len - 2; i >= 0; --i)
        {
            if (ratings[i] > ratings[i + 1])
            {
                right = right + 1;
            }
            else
                right = 1;
                sum += max(left[i], right);
        }
        return sum;
    }
};

O(1)空间

class Solution {
public:
    int candy(vector<int>& ratings) 
    {
        int n = ratings.size();
        int ret = 1;
        int inc = 1, dec = 0, pre = 1;
        for (int i = 1; i < n; i++) 
        {
            if (ratings[i] >= ratings[i - 1]) 
            {
                dec = 0;
                pre = ratings[i] == ratings[i - 1] ? 1 : pre + 1;
                ret += pre;
                inc = pre;
            } 
            else 
            {
                dec++;
                if (dec == inc) 
                {
                    dec++;
                }
                ret += dec;
                pre = 1;
            }
        }
        return ret;
    }
};