leetcode-algorithm/Candy/Candy.cpp at master · assassint2017/leetcode-algorithm · GitHub

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// 贪心，思路一，两次遍历，时间复杂度为on，空间复杂度为on
// 16ms 98.84%

class Solution {
public:
    int candy(vector<int>& ratings)
    {
        // 每个孩子至少有一颗糖
        int *numCandy = new int[ratings.size()]();
        for (int i = 0; i < ratings.size(); i++)
           numCandy[i]++;

        // 从左向右遍历
        for (int i = 1; i < ratings.size(); i++)
        {
            if (ratings[i] > ratings[i - 1])
                numCandy[i] = numCandy[i - 1] + 1;
        }

        // 从右向左遍历
        for (int i = ratings.size() - 2; i >= 0; i--)
        {
            if (ratings[i] > ratings[i + 1] && numCandy[i] <= numCandy[i + 1])
                numCandy[i] = numCandy[i + 1] + 1;
        }

        // 求和
        int sum = 0;
        for (int i = 0; i < ratings.size(); i++)
            sum += numCandy[i];

        delete[] numCandy;
        return sum;
    }
};

// 思路二的时间复杂度为on，空间复杂度为o1
// 16ms 98.84%
#include <vector>
using namespace std;

class Solution {
public:
    int candy(vector<int>& ratings) {
        int sum = 1, pre = 1, count = 1;

        for (int i = 1; i < ratings.size(); i++)
        {
            if (ratings[i] >= ratings[i - 1])
            {
                if (count > 1)
                {
                    sum += count * (count - 1) / 2;
                    if (pre < count)
                        sum += (count - pre);
                    pre = 1;
                }

                if (ratings[i] == ratings[i - 1])
                    pre = 0;

                sum += (++pre);
                count = 1;
            }
            else
                count++;
        }

        if (count > 1)
        {
            sum += count * (count - 1) / 2;
            if (pre < count)
                sum += (count - pre);
        }
        return sum;
    }
};