leetcode 每日打卡 字符串问题

592. 分数加减运算

leetcode-cn.com/problems/fr…

• 正则表达式 正前瞻 exp1(?=exp2)：查找 exp2 前面的 exp1。 exp1(?!exp2)：查找后面不是 exp2 的 exp1。
• 正则表达式 正后顾 (?<=exp2)exp1：查找 exp2 后面的 exp1。(?<!exp2)exp1：查找前面不是 exp2 的 exp1。

/**
 * @param {string} expression
 * @return {string}
 */
var fractionAddition = function(expression) {
    const reg = /[\-\+]?[0-910]+\/[0-910]+/g
    const matchs = expression.match(reg)
    const numeratorReg = /\*{1}(?=\/)/g
    const denominatorReg = /(?<=\/)\*/
    const stack = []    
    let res = matchs[0]
    for(let i=0;i<matchs.length;i++){
        while(stack.length){
            const curr = stack.pop()
            res = calcRes(curr,matchs[i])
        }
        stack.push(res)
    }
    
    function calcRes(num1,num2){
        let [numerator1,denominator1] = num1.split("\/")
        let [numerator2,denominator2] = num2.split("\/")
        let denominatorRes = Number(denominator1) * Number(denominator2)
        let numeratorRes = Number(numerator1) * Number(denominator2) + Number(numerator2) * Number(denominator1)
        let i =2
        while(i<= Math.abs(numeratorRes)){
            if(numeratorRes % i ===0 && denominatorRes % i ===0){
                numeratorRes = numeratorRes/i
                denominatorRes = denominatorRes/i
            }else{
                i++
            }
        }
        if(numeratorRes ==0){
            denominatorRes = 1
        }
        return `${numeratorRes}/${denominatorRes}`
    }
    return res
};

640. 求解方程

leetcode-cn.com/problems/so…

/**
 * @param {string} equation
 * @return {string}
 */
var solveEquation = function (equation) {
    equation = "+" + equation
    let euqaIndex = equation.indexOf("=")
    const reverseReg = /[\-\+]/g
    let left = equation.slice(0, euqaIndex)
    let right = ("+" + equation.slice(euqaIndex + 1)).replace(reverseReg, (match, p1, p2) => {
        if (match === "+") return "-"
        if (match === "-") return "+"
    })
    let transEquation = left + right
    let patten1 = /[\+\-]{1}[0-9]*x/g
    let filteredTransEquation = transEquation.replace(patten1,"")
    let sumPatten = /\+[0-9]+/g
    let diffPatten = /\-[0-9]+/g
    const sumMatch = filteredTransEquation.match(sumPatten) || []
    const diffMatch = filteredTransEquation.match(diffPatten) || []
    let sum = 0
    let sum2 = 0    
    sumMatch.concat(diffMatch).forEach(num => {
        sum = sum + Number(num)
    })

    const mutiplyMatch = transEquation.match(patten1)
    if (mutiplyMatch) {
        for (let i = 0; i < mutiplyMatch.length; i++) {
            if (mutiplyMatch[i] === "+x") {
                sum2++
                continue
            }
            if (mutiplyMatch[i] === "-x") {
                sum2--
                continue
            }
            sum2 = Number(mutiplyMatch[i].match(sumPatten)) + Number(mutiplyMatch[i].match(diffPatten)) + sum2

        }
    }


    if (sum2 === 0) {
        if (sum === 0) {
            return "Infinite solutions"
        } else {
            return "No solution"
        }
    }
    return "x=" + (-sum / sum2)

};