JavaScript如何统计数组同值并计算袜子可配对数量

需求规则 #

• 数组中1对应红色袜子、2对应白色袜子、3对应棕色袜子
• 每2只同色袜子计为1对，同色袜子总数量除以2的整数结果就是该色的配对数

现有代码 #

const stok = [1,1,2,2,3,3,3,3];

function sockMerchant() {
    const colors = ["","red","white","brown"]; 
    const count = stok => stok.reduce((prev, curr) => (prev[curr] = ++prev[curr] || 1, prev), {}); 
    
    const strings = Object.entries(count(stok)).reduce((acc,[key,val]) => (acc[colors[key]] = val , acc),[]); 

    return strings;
    
}

console.log(sockMerchant(stok))

输出差异 #

• 当前输出：[red: 2, white: 2, brown: 4]
• 期望输出：[red: 1, white: 1, brown: 2]

核心修改逻辑是在统计完单类袜子总数后，对数值做除以2的整数运算，你只需要修改reduce中的赋值逻辑即可，修改后完整代码如下：

const stok = [1,1,2,2,3,3,3,3];

function sockMerchant() {
    const colors = ["","red","white","brown"]; 
    const count = stok => stok.reduce((prev, curr) => (prev[curr] = ++prev[curr] || 1, prev), {}); 
    // 仅修改赋值逻辑，对总数量做除以2向下取整得到配对数
    const strings = Object.entries(count(stok)).reduce((acc,[key,val]) => (acc[colors[key]] = Math.floor(val / 2) , acc),[]); 

    return strings;
    
}

console.log(sockMerchant(stok))

如果追求更简洁的写法，也可以用位运算val >> 1替代Math.floor(val / 2)，二者对于正整数的计算结果完全一致。

内容的提问来源于stack exchange，提问作者adtybrhn