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const socketsTypeA = [20, 20] // 1
const socketsTypeB = [2, 20, 3, 40, 50, 50, 60, 70] // 1
const socketsTypeC = [25, 281, 306, 4, 250, 25, 771, 306, 306, 25, 4, 25, 281] // 5


function countDoubleSocketsNumber(sockets) {
    let doubleSocketsNumber = 0, tmp = 0, isCompared = null, compareRecord = [], socketsTypeNumber = []
    sockets.forEach(socket => {
        // isCompared: 是一個 Boolean，藉由 compareRecord 來判斷之前是否比對過該種類的襪子，若 isCompared 為 true，則會在下列 if 跳出
        isCompared = compareRecord.find(element => { return element === socket })
        if (isCompared) return;
        sockets.forEach(otherSocket=> {
            // 該襪子種類若等於其他的襪子，則 tmp +1 
            tmp += (socket === otherSocket)   
        })
        // 將比對紀錄納入 compareRecord
        compareRecord.push(socket)
        // 將該種類襪子總數納入 socketsTypeNumber 中，比如說比對後只有 1 隻，就放入 1
        if(tmp) socketsTypeNumber.push(tmp)
        tmp = 0
    })
    // 一個 index 代表一種，將每種的襪子隻數 / 2 取整數並加總，就可以算出總共幾雙
    socketsTypeNumber.forEach(element => {
        doubleSocketsNumber += Math.floor(element / 2)
    })
    console.log(doubleSocketsNumber) 
}

countDoubleSocketsNumber(socketsTypeA) 
countDoubleSocketsNumber(socketsTypeB)
countDoubleSocketsNumber(socketsTypeC)

/* 原本寫的
for (let i = 0; i < socketsNumber ; i++) {
    isCompared = compareRecord.find(element => {
        return element === sockets[i]
    })
    for(let j = 0; j < socketsNumber ; j++) {
        if(!isCompared && sockets[i] === sockets[j]) {
            tmp++
        }
    }
    compareRecord.push(sockets[i])
    if(tmp) socketsTypeNumber.push(tmp)
    tmp = 0
}
//console.log(socketsTypeNumber)
socketsTypeNumber.forEach(element => {
    doubleSocketsNumber += Math.floor(element / 2)
})
return doubleSocketsNumber
*/