2020-03-18 四则运算

[fanmingfei]

function calculator (string) {
// ...
}

请不要使用eval/Function等

calculator('1 + 2 +3+4') // 10
calculator('1 * 2 + 3 * 4') // 14
calculator('1+2* 3+4') // 11
calculator('1+ 2* 3*4') // 25
calculator('1+2+3/4') // 3.75
calculator('1/2+3+4') // 7.5
calculator('1+2/3+4') // 5.6666666666666
calculator('1+2-3+4') // 4
calculator('1+2+3-4') // 2
calculator('1-2+3+4') // 6
calculator('1+2-3*4') // -9
calculator('1 / 2 / 3 / 4') // 0.04

[LiZhaji]

function map(a, operator, b) {
  switch (operator) {
    case "+":
      return a + b;
    case "-":
      return a - b;
    case "*":
      return a * b;
    case "/":
      return a / b;
  }
}

function cal(string, regWithNum, reg) {
  return string
    .replace(/\s/g, "") // 去空格
    .replace(/\+\-|\-\+/, "-") // 去除多余符号 如1+-3 -> 1-3
    .replace(regWithNum, match => {
      const matches = match.split(reg);

      // 从后往前取，-1+2
      const b = matches.pop();
      const operator = matches.pop();
      const a = matches.join("");

      return map(+a, operator, +b);
    });
}

// \-?\d+\.?\d* 匹配数字
function mulOrDev(string) {
  return cal(string, /\-?\d+\.?\d*[\*\/]\-?\d+\.?\d*/, /([\*\/])/);
}
function addOrDel(string) {
  return cal(string, /\-?\d+\.?\d*[\+\-]\-?\d+\.?\d*/, /([\+\-])/);
}

function calculator(string) {
  // () 有括号情况，未考虑

  // 乘除
  while (string.search(/[\*\/]/) > -1) {
    string = mulOrDev(string);
  }

  // 加减
  // 结果为负数避免进入死循环
  const numReg = /\-?\d+\.?\d*/g;
  while (string.match(numReg).length > 1 && string.search(/[\+\-]/) > -1) {
    string = addOrDel(string);
  }
  return +string;
}

const test = [
  "1 + 2 +3+4",
  "1 * 2 + 3 * 4",
  "1+2* 3+4",
  "1+2+3/4",
  "1/2+3+4",
  "1+2/3+4",
  "1+2-3+4",
  "1-2+3+4",
  "1+2-3*4",
  "1 / 2 / 3 / 4"
];
test.forEach(str => console.log(calculator(str)));

[wangshouren7]

感觉头发掉了几根

function calculator(string) {
    const stringAry = string.split('').filter(s => s !== ' ');

    //中缀表达式转后缀表达式
    let postfix_stack = [], char_ary = [], current;//定义后缀表达式和符号栈
    // console.log(stringAry);

    while (current = stringAry.shift()) {
        if (isNaN(current)) {
            //处理符号
            if (current === ')') {
                addUntilRight(postfix_stack, char_ary);
            } else if (higher(char_ary[char_ary.length - 1], current)) {
                addChar(postfix_stack, char_ary, current)
            } else {
                char_ary.push(current);//4
            }
        } else {
            //处理数字
            postfix_stack.push(current);//  1   /
        }

    }
    postfix_stack = postfix_stack.concat(char_ary.reverse());


    //后缀表达式计算结果
    const num_stack = [];

    while (postfix_stack.length > 0 && (current = postfix_stack.shift())) {

        if (isNaN(current)) {
            //运算符
            compute(num_stack, current);
        } else {
            //数字
            num_stack.push(current);// 
        }
    }
    console.log(num_stack.pop());


}

function addChar(postfix_stack, char_ary, current) {

    let _operator = current;

    if (current === '*' || current === '/') {
        current = char_ary[char_ary.length - 1];
        if (current !== '+' && current !== '-' && current !== undefined) {
            while ((current = char_ary.pop()) && (current !== '+' && current !== '-')) {
                postfix_stack.push(current);
            }
            char_ary.push(current);
        }
        char_ary.push(_operator)
    } else {
        postfix_stack.push(...char_ary.reverse())
        char_ary.splice(0, char_ary.length, current);
    }
}
function compute(num_stack, current) {
    const a = num_stack.pop(), b = num_stack.pop()
    switch (current) {
        case '+':
            // console.log(`${index++}:${b}+${a}`);
            num_stack.push(+b + +a);

            break;
        case '-':
            // console.log(`${index++}:${b}-${a}`);

            num_stack.push(b - a);
            break;
        case '*':
            // console.log(`${index++}:${b}*${a}`);

            num_stack.push(b * a);
            break;
        case '/':
            // console.log(`${index++}:${b}/${a}`);
            num_stack.push(b / a);
            break;
    }
}
function addUntilRight(postfix_stack, char_ary) {
    let current;
    while ((current = char_ary.pop()) && current !== '(') {
        postfix_stack.push(current)
    }
}
function higher(c, current) {

    if (current === '+' || current === '-' || current === '(') {
        return true
    }
    if (current === '*' || current === '/') {

        return !(c === '+' || c === '-')
    }
    return true;
}


calculator('1 + 2 +3+4') // 10
calculator('1 * 2 + 3 * 4') // 14
calculator('1+2* 3+4') // 11
calculator('1+ 2* 3*4') // 25
calculator('1+2+3/4') // 3.75
calculator('1/2+3+4') // 7.5
calculator('1+2/3+4') // 5.6666666666666
calculator('1+2-3+4') // 4
calculator('1+2+3-4') // 2
calculator('1-2+3+4') // 6
calculator('1+2-3*4') // -9
calculator('1 / 2 / 3 / 4') // 0.04