LeetCode：Candy

题目链接：Candy

There are N children standing in a line. Each child is assigned a rating value.
You are giving candies to these children subjected to the following requirements:

• Each child must have at least one candy.
• Children with a higher rating get more candies than their neighbors.

What is the minimum candies you must give?

第一次解题思路：

public class Solution {
    public int candy(int[] ratings) {
        if (ratings == null || ratings.length == 0) {
            return 0;
        }
        int[] num = new int[ratings.length];
        num[0] = 1;
        for (int i=1; i<ratings.length; i++) {
            // 后一个比前一个得分小
            if (ratings[i] < ratings[i-1]) {
                num[i] = 1;
                for (int j=i; j>0; j--) {
                    if (ratings[j] < ratings[j-1] && num[j] == num[j-1]) {
                        num[j-1]++;
                    } else {
                        break;
                    }
                }
            } else if (ratings[i] == ratings[i-1]) {
                num[i] = 1;
            } else {
                num[i] = num[i-1]+1;
            }
        }

        int sum = 0;
        for (int i:num ) {
            sum += i;
        }

        return sum;
    }
}

提交后执行测试例超时，经过分析，觉得应该是前面的嵌套循环太耗时（因为每走一步都要往回看一下），考虑优化一下。

第二次解题思路：

public class Solution {
    public int candy(int[] ratings) {
        if (ratings == null || ratings.length == 0) {
            return 0;
        }
        int sum = 0;
        // 局部降序序列起始位置预分配的糖果数
        int localFirstPosVal = 1;
        // 局部降序序列的长度
        int localDescSeqLen = 1;
        for (int i=1; i<ratings.length; i++) {
            // 后一个比前一个得分小
            if (ratings[i] < ratings[i-1]) {
                localDescSeqLen++;
            } else {
                sum = getDesSeqSum(localFirstPosVal, localDescSeqLen, sum);

                if (ratings[i] == ratings[i-1]) {
                    localFirstPosVal = 1;
                } else if (ratings[i] > ratings[i-1] && localDescSeqLen > 1) {
                    localFirstPosVal = 2;
                } else if (ratings[i] > ratings[i-1] && localDescSeqLen == 1) {
                    localFirstPosVal += 1; 
                }
                localDescSeqLen = 1;
            } 
        }

        return getDesSeqSum(localFirstPosVal, localDescSeqLen, sum);
    }
    // 计算降序序列的糖果总数
    public int getDesSeqSum(int localFirstPosVal, int localDescSeqLen, int sum) {
        if (localDescSeqLen >= localFirstPosVal) {
            sum += (1+localDescSeqLen)*localDescSeqLen/2;
        } else {
            sum += localFirstPosVal;
            sum += localDescSeqLen*(localDescSeqLen-1)/2;
        }
        return sum;
    }
}

暂时先这样吧，后面有时间再改进改进。。。