题解 | #24点运算#

穷举主要就是排列组合问题 而排列组合主要就是全排列，这里用到了递归进行逐级的全排列 但是可重复的全排列没想好怎么写，暂时只能用了三层循环

var line
while (line = readline()){
    var matchFlag = false
    var params = line.split(" ")
    //过滤大小王
    if(params.includes("JOKER")||params.includes("joker")) {
        print("ERROR")
        break
    }
    //数据处理
    params = params.map(item => {
        switch(item) {
            case "J":
                return 11
            case "Q":
                return 12
            case "K":
                return 13
            case "A":
                return 1
            default:
                return parseInt(item)
        }
    })
    //数字序列生成
    var arrangeArr = allArrangement(params)
    
    //运算符序列生成
    var opt = ["+","-","*","/"]
    var optArrangeArr = everyArrangement(["+","-","*","/"])

    arrangeArr.forEach(digits => {
        optArrangeArr.forEach(opts => {
            var result = digits[0] 
            for(let i=0;i<3;i++) {
                switch(opts[i]) {
                    case "+":
                        result += digits[i+1]
                        break
                    case "-":
                        result -= digits[i+1]
                        break
                    case "*":
                        result *= digits[i+1]
                        break
                    case "/":
                        result = (result - result % digits[i+1]) / digits[i+1]
                        break
                }
            }
            if (result == 24 && !matchFlag) {
                digits = digits.map(item => {
                    switch(item) {
                        case 11:
                            return "J"
                        case 12:
                            return "Q"
                        case 13:
                            return "K"
                        case 1:
                            return "A"
                        default:
                            return parseInt(item)
                    }
                })
                print(`${digits[0]}${opts[0]}${digits[1]}${opts[1]}${digits[2]}${opts[2]}${digits[3]}`)
                matchFlag = true
            }
        })
    })

    if (!matchFlag) {
        print("NONE")
    }
    
}

//不重复全排列
function allArrangement(arr) {
    if (arr.length == 1) return [[arr[0]]]
    var result = []
    arr.forEach((newItem,index) => {
        var otherArr = arr.slice(0,index).concat(arr.slice(index+1))
        
        allArrangement(otherArr).forEach(beforeItem => {
            result.push(beforeItem.concat([newItem]))
        })
    })
    return result
}

//可重复全排列
function everyArrangement(arr) {
    var result = []
    arr.forEach(item1 => {
        arr.forEach(item2 => {
            arr.forEach(item3 => {
                result.push([item1,item2,item3])
            })
        })
    })
    return result
}