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2759. Convert JSON String to Object

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

• 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();
  }
  
  

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