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141 | type JSONValue =
| null
| boolean
| number
| string
| JSONValue[]
| { [key: string]: JSONValue };
class JSONParser {
private str: string;
private i: number;
constructor(str: string) {
this.str = str;
this.i = 0;
}
public parse(): JSONValue {
return this.parseValue();
}
private parseValue(): JSONValue {
switch (this.str[this.i]) {
case '{':
return this.parseObject();
case '[':
return this.parseArray();
case 't': // true
case 'f': // false
case 'n': // null
return this.parseLiteral();
case '"':
return this.parseString();
default:
return this.parseNumber();
}
}
private parseObject(): JSONValue {
++this.i;
const ans: JSONValue = {};
while (this.i < this.str.length && this.str[this.i] !== '}') {
const key = this.parseString();
this.expectChar(':');
const value = this.parseValue();
ans[key] = value;
if (this.str[this.i] === ',') {
++this.i;
}
}
++this.i;
return ans;
}
private parseArray(): JSONValue[] {
++this.i;
const ans: JSONValue[] = [];
while (this.i < this.str.length && this.str[this.i] !== ']') {
const value = this.parseValue();
ans.push(value);
if (this.str[this.i] === ',') {
++this.i;
}
}
++this.i;
return ans;
}
private parseLiteral(): boolean | null {
if (this.str.startsWith('true', this.i)) {
this.i += 4;
return true;
}
if (this.str.startsWith('false', this.i)) {
this.i += 5;
return false;
}
if (this.str.startsWith('null', this.i)) {
this.i += 4;
return null;
}
throw new Error(`Unexpected token at position ${this.i}`);
}
private parseString(): string {
let ans = '';
++this.i;
while (this.i < this.str.length && this.str[this.i] !== '"') {
ans += this.str[this.i];
++this.i;
}
++this.i;
return ans;
}
private parseNumber(): number {
let start = this.i;
if (this.str[this.i] === '-') {
++this.i;
}
while (this.i < this.str.length && this.isDigit(this.str[this.i])) {
++this.i;
}
if (this.str[this.i] === '.') {
++this.i;
while (this.i < this.str.length && this.isDigit(this.str[this.i])) {
++this.i;
}
}
return Number(this.str.slice(start, this.i));
}
private isDigit(n: string): boolean {
return n >= '0' && n <= '9';
}
private expectChar(char: string): void {
if (this.str[this.i] !== char) {
throw new Error(`Expected '${char}' at position ${this.i}`);
}
++this.i;
}
}
function jsonParse(str: string): JSONValue {
const parser = new JSONParser(str);
return parser.parse();
}
|
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