q2 = input => { let tree = []; let stack = []; input = input.split(''); // parse nrs and strip spaces const input2 = []; for (let i = 0; i < input.length; i++) { let nr = input[i].charCodeAt() - 48; if (nr >= 0 && nr < 10) { while ( ++i < input.length && input[i].charCodeAt() > 47 && input[i].charCodeAt() < 58 ) { nr = nr * 10 + input[i].charCodeAt() - 48; } input2.push(BigInt(nr)); i--; } else if (input[i] === " ") { continue; } else { input2.push(input[i]); } } input = input2; // parenthesis for (let i = 0; i < input.length; i++) { let token = input[i]; if (token === "(") { stack.push(tree); tree = []; } else if (token === ")") { const tree0 = stack.pop(); tree0.push(tree); tree = tree0; } else { tree.push(token); } } // * const walkTreeMul = ast => { let mul = []; for (let i = 0; i < ast.length; i++) { if (Array.isArray(ast[i])) ast[i] = walkTreeMul(ast[i]); else if (ast[i] === "*") mul.push(i); } if (!mul.length) return ast; let out = ["*"]; let j = 0; for (let i = 0; i < mul.length; i++) { const k = mul[i]; out.push(ast.slice(j, k)); j = k + 1; } out.push(ast.slice(j)); return out; }; tree = walkTreeMul(tree); // + const walkTreePlus = ast => { let sum = []; for (let i = 0; i < ast.length; i++) { if (Array.isArray(ast[i])) ast[i] = walkTreePlus(ast[i]); else if (ast[i] === "+") sum.push(i); } if (!sum.length) return ast; let out = ["+"]; let j = 0; for (let i = 0; i < sum.length; i++) { const k = sum[i]; out.push(ast.slice(j, k)); j = k + 1; } out.push(ast.slice(j)); return out; }; tree = walkTreePlus(tree); // I could try to remember why I end up with // nested arrays and handroll my parser better // or I can inline const inline = ast => { if (Array.isArray(ast[0])) return inline(ast[0]); for (let i = 1; i < ast.length; i++) { ast[i] = inline(ast[i]); } return ast; }; tree = inline(tree); // return tree; const calc = ast => { let prefix = ast[0]; if (typeof prefix === "bigint") return prefix; else { let acc = calc(ast[1]); if (prefix === "*") { for (let i = 2; i < ast.length; i++) { acc *= calc(ast[i]); } } else if (prefix === "+") { for (let i = 2; i < ast.length; i++) { console.log({ i, acc }); acc += calc(ast[i]); } } else { return "there be either bugs or bad input here"; } return acc; } }; return { tree, res: calc(tree) }; }