packageeasy;

publicclassAddStrings {

publicstaticStringaddStrings(Stringnum1,Stringnum2) {

if(num1 ==null ||num1.length() ==0)returnnum2;

elseif(num2 ==null ||num2.length() ==0)returnnum1;

inti =num1.length()-1,j =num2.length()-1;

longcarry =0,sum =0;

StringBuildersb =newStringBuilder();

char[]char1 =num1.toCharArray();

char[]char2 =num2.toCharArray();

while(i >=0 ||j >=0){

sum =carry;

if(i >=0)sum +=Character.getNumericValue(char1[i--]);

if(j >=0)sum +=Character.getNumericValue(char2[j--]);

carry =sum/10;

sb.append(sum%10);

}

if(carry !=0)sb.append(carry);

returnsb.reverse().toString();

}

publicstaticvoidmain(String...args){

Stringnum1 ="9";

Stringnum2 ="99";

System.out.println(addStrings(num1,num2));

}

}

| # | Title | Solutions | Time | Space | Difficulty | Tag | Notes

|-----|--------------------------|---------------------|-------|--------|------------|-----|------

|415|[Add Strings](https://leetcode.com/problems/add-strings/)|[Solution](../../blob/master/EASY/src/easy/AddStrings.java)| O(n)|O(1)| Easy|

|350|[Intersection of Two Arrays II](https://leetcode.com/problems/intersection-of-two-arrays-ii/)|[Solution](../../blob/master/EASY/src/easy/IntersectionOfTwoArraysII.java)| O(m+n)|O((m+n)) could be optimized | Easy| HashMap, Binary Search

|349|[Intersection of Two Arrays](https://leetcode.com/problems/intersection-of-two-arrays/)|[Solution](../../blob/master/EASY/src/easy/IntersectionOfTwoArrays.java)| O(m+n)|O(min(m,n)) | Easy| Two Pointers, Binary Search

|325|[Maximum Size Subarray Sum Equals k](https://leetcode.com/problems/maximum-size-subarray-sum-equals-k/)|[Solution] | O(n)|O(n) | Medium| HashMap