# Remove All Adjacent Duplicates In String

Given a string S of lowercase letters, a duplicate removal consists of choosing two adjacent and equal letters, and removing them.

We repeatedly make duplicate removals on S until we no longer can.

Return the final string after all such duplicate removals have been made. It is guaranteed the answer is unique.

Example 1:

```
Input: "abbaca"
Output: "ca"
Explanation:
For example, in "abbaca" we could remove "bb" since the letters are adjacent
and equal, and this is the only possible move. The result of this move is
that the string is "aaca", of which only "aa" is possible, so the final
string is "ca".
```

### Solution

```
/**
* @param {string} S
* @return {string}
* @time complexity: O(n) where n is the length of S
* @space complexity: O(n)
*/
var removeDuplicates = function(S) {
const stack = [];
for (let c of S) {
if (c !== stack[stack.length - 1]) {
stack.push(c);
} else {
stack.pop();
}
}
return stack.join('');
};
```

### Alternative Solution

```
/**
* @param {string} S
* @return {string}
* @time complexity: O(n) where n is the length of S
* @space complexity: O(n)
*/
var removeDuplicatesAlternative = function(S) {
const arr = S.split('');
for (let i = 1; i < arr.length; i++) {
if (arr[i] === arr[i-1]) {
arr.splice(i-1, 2);
i -= 2;
}
}
return arr.join('');
};
```

### Test Case

```
const assert = require('chai').assert;
describe('Remove All Adjacent Duplicates In String', () => {
it('should return \'ca\' when \'abbaca\' is given', () => {
assert.strictEqual(removeDuplicates('abbaca'), 'ca');
});
it('should return \'\' when \'aabbacca\' is given', () => {
assert.strictEqual(removeDuplicates('aabbacca'), '');
});
it('should return \'\' when \'\' is given', () => {
assert.strictEqual(removeDuplicates(''), '');
});
});
```

```
Remove All Adjacent Duplicates In String
✓ should return 'ca' when 'abbaca' is given
✓ should return '' when 'aabbacca' is given
✓ should return '' when '' is given
3 passing (12ms)
```