Added Java and Cpp Code

Unique_String.java

// Java Code
import java.util.HashMap;
import java.util.Map;

// Time Complexity: O(n) 
// Space Complexity: O(n) 
// where n = length of string
class Solution {
    public static final int MAX_UNICODE = 65_535;
    public static boolean checkWhetherStringIsUnique(String string) {
        Map<Character, Boolean> characters = new HashMap<>();
        int start = 0;
        while(start < string.length()) {
            int ascii = string.charAt(start)+0;
            if(ascii > MAX_UNICODE) {
                System.out.println("INVALID VALUE");
                break;
            } else {
                if(string.charAt(start) == ' ') start++; //ignoring whitespace
                else {
                    // checking if character is present in map or not
                    if(characters.containsKey(string.charAt(start))) return false;
                    else {
                        characters.put(string.charAt(start), false);
                        start++;
                    }
                }
            }
        }
        return true;
    }
}

class Scratch {

    public static void main(String[] args) {
        Solution solution = new Solution();
        System.out.println(solution.checkWhetherStringIsUnique("Shivam"));
        System.out.println(solution.checkWhetherStringIsUnique("Competative Programming"));
        System.out.println(solution.checkWhetherStringIsUnique("qwertyui asdf ghjk zxcv bnm"));
    }
}



// C++ Code

#include<bits/stdc++.h>
using namespace std;
#define MAX_UNICODE 65535

// Time Complexity: O(n) 
// Space Complexity: O(n) 
// where n = length of string
bool checkWhetherStringIsUnique(string);

int main() {
	if(checkWhetherStringIsUnique("Competative Programming")) {
		cout << "true" << endl;
	} else {
		cout << "false" << endl;
	}	

	if(checkWhetherStringIsUnique("QWERTY UIOP LKJH FDSA ZXCV")) {
		cout << "true" << endl;
	} else {
		cout << "false" << endl;
	}	
	return 0;
}

bool checkWhetherStringIsUnique(string value) {
	unordered_map<char,bool> checking;	
	for(auto chars : value) {
		int ascii = chars+0;
		if(ascii > MAX_UNICODE) {
			cout << "INVALID VALUE" << endl;
			break;
		} else {

			if(chars == ' ') continue; //ignoring whitespace
			else {
				// checking if character is present in map or not
				if(checking.find(chars) != checking.end()) return false;
				else {
					checking[chars] == false;
				}
			}
		}
	}
	return true;
}