Add Strings LeetCode

Given two non-negative numbers num1 and num2 represented as string, return the sum of num1 and num2.

NOTE:

• The length of both num1 and num2 is < 5100.
• Both num1 and num2 contains only digits 0-9.
• Both num1 and num2 does not contain any leading zero.
• You must not use any built-in BigInteger library or convert the inputs to integer directly.

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Solution

	/**
	*
	* Given two non-negative numbers num1 and num2 represented as string, return the sum of num1 and num2.
	Note:
	The length of both num1 and num2 is < 5100.
	Both num1 and num2 contains only digits 0-9.
	Both num1 and num2 does not contain any leading zero.
	You must not use any built-in BigInteger library or convert the inputs to integer directly.
	*
	*
	* @author rbaral
	*/
	public class AddStrings {
	public static String addStrings(String num1, String num2) {
	String totalSum = "";
	int sum = 0, carry = 0;
	int num2Index = num2.length()-1;
	int num1Index = num1.length()-1;
	for(num1Index=num1.length()-1; num1Index>=0;num1Index--){
	sum = 0;
	if(num2Index>=0){//till there are chars in both strings
	sum = num1.charAt(num1Index) -'0' + num2.charAt(num2Index)-'0' + carry;
	num2Index--;
	if(sum>9){
	carry = 1;
	sum = sum - 10;
	}else{
	carry = 0;
	}
	totalSum= sum + totalSum;
	}else
	break;
	}
	//if the num1 is exhausted and num2 has some chars
	if(num2Index>=0){
	//simply add the remaining portion of num2 with the carry and append to the totalSum so far
	num2 = num2.substring(0, num2Index+1);
	for(int i = num2.length()-1; i>=0;i--){
	sum = num2.charAt(i) - '0' + carry;
	if(sum>9){
	carry = 1;
	sum = sum - 10;
	totalSum = sum + totalSum;
	}else{
	//simply append the sum to the remaining chars of num2 and break
	totalSum= sum +totalSum;
	carry = 0;
	}
	}
	}else if(num1Index>=0){
	num1 = num1.substring(0, num1Index+1);
	System.out.println("remaining num1:"+num1+" sum "+totalSum+" cary "+carry);
	for(int i= num1.length()-1;i>=0;i--){
	sum = num1.charAt(i) - '0' + carry;
	if(sum>9){
	carry = 1;
	sum = sum -10;
	totalSum= sum + totalSum;
	}else{
	totalSum= sum +totalSum;
	carry = 0;
	}
	}
	}
	if(carry>0){
	totalSum = carry+totalSum;
	}
	return totalSum;
	}
	public static void main(String args[]){
	String num1 = "19";
	String num2 = "9";
	System.out.println(addStrings(num1, num2));
	System.out.println(addStrings("0", "0"));
	System.out.println(addStrings("99", "99"));
	System.out.println(addStrings("6994", "36"));
	}
	}

view raw AddStrings.java hosted with ❤ by GitHub