【HackerRank 1 Week Preparation Kit】01-Plus Minus - Noelle Mu | SRE | Open Source

前言

发现了一个很好玩的英文 OJ：HackerRank，听说在国外蛮火的。这个 OJ 支持 Golang，题目是全英文，自带的编辑器有代码提示和自动补全功能体验非常好（LeetCode 的智能模式至今没支持 Golang。。。），也有一些刷题计划可以选择，正好拿来练练英文阅读能力。

而且刷了这么久的 LeetCode，真的是被核心代码模式惯坏了，对 ACM 模式一无所知，完全不会读输入输出，是时候找几个 ACM 模式的 OJ 练练手了。

题目原文

Given an array of integers, calculate the ratios of its elements that are positive, negative, and zero. Print the decimal value of each fraction on a new line with 6 places after the decimal.

Note: This challenge introduces precision problems. The test cases are scaled to six decimal places, though answers with absolute error of up to 10^-4 are acceptable.

Example

arr = [1, 1, 0, -1, -1]

There are elements, two positive, two negative and one zero. Their ratios are 2/5 = 0.400000, 2/5 = 0.400000 and 1/5 = 0.200000. Results are printed as:

0.400000
0.400000
0.200000

Function Description

Complete the plusMinus function in the editor below.

plusMinus has the following parameter(s):

int arr[n]: an array of integers
Print
Print the ratios of positive, negative and zero values in the array. Each value should be printed on a separate line with 6 digits after the decimal. The function should not return a value.

Input Format

The first line contains an integer, n, the size of the array.
The second line contains n space-separated integers that describe arr[n].

Constraints

• 0 < n <= 100
• -100 <= arr[i] <= 100

Output Format

Print the following 3 lines, each to 6 decimals:

1. proportion of positive values
2. proportion of negative values
3. proportion of zeros

Sample Input

STDIN Function

---

6 arr[] size n = 6
-4 3 -9 0 4 1 arr = [-4, 3, -9, 0, 4, 1]

Sample Output

0.500000
0.333333
0.166667

Explanation

There are 3 positive numbers, 2 negative numbers, and 1 zero in the array.
The proportions of occurrence are positive: 3/6 = 0.500000, negative: 2/6 = 0.333333 and zeros: 1/6 = 0.166667.

难度

Easy

解题思路

入门题，题目的大概含义就是求出 arr 中正数、负数和零在数组中的比重，分别统计然后除以数组长度并按要求打印出来即可，注意类型转换。

复杂度分析

时间复杂度：O(n)，需要遍历数组一次。

空间复杂度：O(1)，只使用了常数个数的存储空间。

AC 代码

func plusMinus(arr []int32) {
    // Write your code here
    n := float64(len(arr))
    negatives, positives, zeros := 0.0, 0.0, 0.0
    for _, num := range arr {
        if num < 0 {
            negatives++
        } else if num > 0 {
            positives++
        } else {
            zeros++
        }
    }
    fmt.Printf("%.6f\n%.6f\n%.6f\n", positives / n, negatives / n, zeros / n)
}