README_EN.md

comments	difficulty	edit_url	tags
true	Hard	https://github.com/doocs/leetcode/edit/main/solution/2700-2799/2759.Convert%20JSON%20String%20to%20Object/README_EN.md	JavaScript

2759. Convert JSON String to Object 🔒

中文文档

Description

Given a string str, return parsed JSON parsedStr. You may assume the str is a valid JSON string hence it only includes strings, numbers, arrays, objects, booleans, and null. str will not include invisible characters and escape characters. 

Please solve it without using the built-in JSON.parse method.

 

Example 1:

Input: str = '{"a":2,"b":[1,2,3]}'
Output: {"a":2,"b":[1,2,3]}
Explanation: Returns the object represented by the JSON string.

Example 2:

Input: str = 'true'
Output: true
Explanation: Primitive types are valid JSON.

Example 3:

Input: str = '[1,5,"false",{"a":2}]'
Output: [1,5,"false",{"a":2}]
Explanation: Returns the array represented by the JSON string.

 

Constraints:

• str is a valid JSON string
• 1 <= str.length <= 105

Solutions

Solution 1

TypeScript

function jsonParse(str: string): any {
    const n = str.length;
    let i = 0;

    const parseTrue = (): boolean => {
        i += 4;
        return true;
    };

    const parseFalse = (): boolean => {
        i += 5;
        return false;
    };

    const parseNull = (): null => {
        i += 4;
        return null;
    };

    const parseNumber = (): number => {
        let s = '';
        while (i < n) {
            const c = str[i];
            if (c === ',' || c === '}' || c === ']') {
                break;
            }
            s += c;
            i++;
        }
        return Number(s);
    };

    const parseArray = (): any[] => {
        const arr: any[] = [];
        i++;
        while (i < n) {
            const c = str[i];
            if (c === ']') {
                i++;
                break;
            }
            if (c === ',') {
                i++;
                continue;
            }
            const value = parseValue();
            arr.push(value);
        }
        return arr;
    };

    const parseString = (): string => {
        let s = '';
        i++;
        while (i < n) {
            const c = str[i];
            if (c === '"') {
                i++;
                break;
            }
            if (c === '\\') {
                i++;
                s += str[i];
            } else {
                s += c;
            }
            i++;
        }
        return s;
    };

    const parseObject = (): any => {
        const obj: any = {};
        i++;
        while (i < n) {
            const c = str[i];
            if (c === '}') {
                i++;
                break;
            }
            if (c === ',') {
                i++;
                continue;
            }
            const key = parseString();
            i++;
            const value = parseValue();
            obj[key] = value;
        }
        return obj;
    };
    const parseValue = (): any => {
        const c = str[i];
        if (c === '{') {
            return parseObject();
        }
        if (c === '[') {
            return parseArray();
        }
        if (c === '"') {
            return parseString();
        }
        if (c === 't') {
            return parseTrue();
        }
        if (c === 'f') {
            return parseFalse();
        }
        if (c === 'n') {
            return parseNull();
        }
        return parseNumber();
    };
    return parseValue();
}