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逆波兰表达式实现四则运算

admin
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2020-11-13 16:50:26 阅读 91

WIKI地址

逆波兰表达式

在线测试

逆波兰计算器

核心代码

const leftBracket = '(' const rightBracked = ')' const ops = { ['+']: { level: 1, calc: (a, b) => a + b }, ['-']: { level: 1, calc: (a, b) => a - b }, ['*']: { level: 2, calc: (a, b) => a * b }, ['/']: { level: 2, calc: (a, b) => a / b }, } function isNumber(v) { return /\d+/.test(v) } function parseExp(express) { let preVal = '' let res = [] for (let i = 0, len = express.length; i < len; i++) { if (isNumber(express[i])) { preVal += express[i] } else { if (preVal) res.push(preVal) res.push(express[i]) preVal = '' } } if (preVal) res.push(preVal) return res } function parseRPN(express) { let res = [] let sop = [] let sopInd = -1 let exps = parseExp(express) exps.forEach(v => { if (isNumber(v)) { res.push(v) } else if (v in ops) { while (sop.length && sop[sopInd] in ops && ops[sop[sopInd]].level >= ops[v].level) { res.push(sop.pop()) sopInd-- } sop.push(v) sopInd++ } else { if (v === leftBracket) { sop.push(v) sopInd++ } if (v === rightBracked) { while (sop.length && sop[sopInd] !== leftBracket) { res.push(sop.pop()) sopInd-- } if (sop.length) { sop.pop() sopInd-- } } } }) while (sop.length) { res.push(sop.pop()) sopInd-- } return res } function calculator(express) { let stack = [] let rpn = parseRPN(express) rpn.forEach(v => { if (isNumber(v)) { stack.push(v) } else if (v in ops) { let n1 = stack.pop() let n2 = stack.pop() stack.push(ops[v].calc(Number(n2), Number(n1))) } }) return stack.pop() }

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