LeetCode-135. Candy (JAVA)根据等级分糖果
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135. Candy(贪心)
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?
N个孩子站成一排,给每个人设定一个权重(已知)。按照如下的规则分配糖果: (1)每个孩子至少分得一颗糖果 (2)权重较高的孩子,会比他的邻居获得更多的糖果。
问:总共最少需要多少颗糖果?请分析算法思路,以及算法的时间,空间复杂度是多少。
假设每个孩子分到的糖果数组为A[N],初始化为{1},因为每个人至少分到一颗糖。
时间复杂度:O(n)
空间复杂度:O(n)
实现:
1、与前面的邻居比较,前向遍历权重数组ratings,如果ratings[i]>ratings[i-1],则A[i]=A[i-1]+1;
2、与后面的邻居比较,后向遍历权重数组ratings,如果ratings[i]>ratings[i+1]且A[i]<A[i+1]+1,则更新A,A[i]=A[i+1]+1;
3、对A求和即为最少需要的糖果。
public int candy(int[] ratings) {int A[] = new int[ratings.length];// 每人至少一个糖果Arrays.fill(A, 1);for (int i = 1; i < ratings.length; i++)if (ratings[i] > ratings[i - 1])A[i] = A[i - 1] + 1;int sum = A[ratings.length - 1];for (int i = ratings.length - 2; i >= 0; i--) {if (ratings[i] > ratings[i + 1] && A[i] <= A[i + 1])// 要比邻居多,并求与邻居相比的取较大值A[i] = A[i + 1] + 1;sum += A[i];}return sum;}
// 分别从两边遍历选取较大值,计算结果public int candy(int[] ratings) {int L[] = new int[ratings.length];int R[] = new int[ratings.length];// 每人至少一个糖果Arrays.fill(L, 1);Arrays.fill(R, 1);for (int i = 1; i < ratings.length; i++)if (ratings[i] > ratings[i - 1])L[i] = L[i - 1] + 1;for (int i = ratings.length - 2; i >= 0; i--) {if (ratings[i] > ratings[i + 1])R[i] = R[i + 1] + 1;}int sum = 0;for (int i = 0; i < ratings.length; i++)sum += Math.max(L[i], R[i]);return sum;}
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