shunting-yard algorithm1

shuntingYard1.ts

//reference https://qiita.com/phenan/items/df157fef2fea590e3fa9

function shuntingYard1(input: string): string {
  let i = 0;
  const stack = ['$'];
  let output = '';
  while (input.length >= i) {
    const c = input.charAt(i)
    if (priority(stack[stack.length - 1]) > priority(c)) {
      output = output + stack.pop();
    } else {
      stack.push(c);
      i++;
    }
  }

  return output;
}

function priority(c: string) {
  switch (c) {
    case '$': return 0;
    case '+': return 1;
    case '*': return 2;
    default: return 3;
  }
}

console.log(shuntingYard1('1+2$'));   // 12+
console.log(shuntingYard1('1*2+3$')); // 12*3+
console.log(shuntingYard1('1+2*3$')); // 123*+