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basic-calculator.ts
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basic-calculator.ts
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const DIGITS = {
"0": 0,
"1": 1,
"2": 2,
"3": 3,
"4": 4,
"5": 5,
"6": 6,
"7": 7,
"8": 8,
"9": 9,
};
const SIGNS = {
"-": -1,
"+": 1,
};
const BRACKETS = {
"(": "(",
")": ")",
};
export function tokenize(s: string): string[] {
let tokens: string[] = [];
let token = "";
for (let i = 0; i < s.length; ++i) {
let c = s[i];
if (c === " ") {
continue;
} else if (c in BRACKETS || c in SIGNS) {
if (token !== "") {
tokens.push(token);
token = "";
}
tokens.push(c);
} else {
// digit
token += c;
}
}
if (token !== "") {
tokens.push(token);
token = "";
}
return tokens;
}
export function computeValue(tokens: readonly string[], l: number, h: number): number {
let i = l;
let result = 0;
let sign: 1 | -1 = 1;
while (i < h) {
if (tokens[i] === "(") {
let openBrackets = 1;
let j = i + 1;
while (openBrackets !== 0) {
if (tokens[j] === "(") ++openBrackets;
else if (tokens[j] === ")") --openBrackets;
++j;
}
let val = computeValue(tokens, i + 1, j - 1);
result += val * sign;
sign = 1;
i = j;
continue;
}
if (tokens[i] in SIGNS) {
sign *= SIGNS[tokens[i] as "+" | "-"];
} else {
// digit
result += Number(tokens[i]) * sign;
sign = 1;
}
++i;
}
return result;
}
export function calculate(s: string): number {
let tokens = tokenize(s);
let result = computeValue(tokens, 0, tokens.length);
return result;
}