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# Shifting Letters II LeetCode Solution

## Problem – Shifting Letters II

You are given a string `s` of lowercase English letters and a 2D integer array `shifts` where `shifts[i] = [starti, endi, directioni]`. For every `i`shift the characters in `s` from the index `starti` to the index `endi` (inclusive) forward if `directioni = 1`, or shift the characters backward if `directioni = 0`.

Shifting a character forward means replacing it with the next letter in the alphabet (wrapping around so that `'z'` becomes `'a'`). Similarly, shifting a character backward means replacing it with the previous letter in the alphabet (wrapping around so that `'a'` becomes `'z'`).

Return the final string after all such shifts to `s` are applied.

Example 1:

``````Input: s = "abc", shifts = [[0,1,0],[1,2,1],[0,2,1]]
Output: "ace"
Explanation: Firstly, shift the characters from index 0 to index 1 backward. Now s = "zac".
Secondly, shift the characters from index 1 to index 2 forward. Now s = "zbd".
Finally, shift the characters from index 0 to index 2 forward. Now s = "ace".``````

Example 2:

``````Input: s = "dztz", shifts = [[0,0,0],[1,1,1]]
Output: "catz"
Explanation: Firstly, shift the characters from index 0 to index 0 backward. Now s = "cztz".
Finally, shift the characters from index 1 to index 1 forward. Now s = "catz".``````

Constraints:

• `1 <= s.length, shifts.length <= 5 * 104`
• `shifts[i].length == 3`
• `0 <= starti <= endi < s.length`
• `0 <= directioni <= 1`
• `s` consists of lowercase English letters.

### Shifting Letters II LeetCode Solution in C++

``````class Solution {
public:
string shiftingLetters(string s, vector<vector<int>>& sh) {
long sz=s.size();
vector<long>line(sz+1,0);
for(auto & i:sh){
// forward shift so do +1
if(i[2]==1){
line[i[0]]++;
line[i[1]+1]--;
}
//backward shift so do -1
else{
line[i[0]]--;
line[i[1]+1]++;
}
}
for(int i=1;i<=sz;i++)
line[i]+=line[i-1];
for(int i=0;i<sz;i++){
// line[i] is how many times i have to increase or decrease the s[i] char.So i am adding it and taking modulo
int increaseBy=(s[i]-'a'+line[i])%26;
// this is to make -ve module +ve.
increaseBy=(increaseBy+26)%26;
s[i]='a'+increaseBy;
}
return s;
}
};
``````

### Shifting Letters II LeetCode Solution in Java

``````  public String shiftingLetters(String s, int[][] shifts) {
char[] ch = s.toCharArray();
int[] count = new int[s.length()+1];

for(int[] shift : shifts){
int value = shift[2] == 1 ? 1 : -1;
count[shift[0]] += value;
count[shift[1] + 1] -= value;
}

int sum = 0;
for(int i = 0; i < count.length - 1; i++){
sum += count[i];
int newChar = ((ch[i] - 'a') + sum) % 26;
if(newChar < 0) newChar+= 26;
ch[i] =  (char)('a' + newChar);
}

return String.valueOf(ch);
}``````

### Shifting Letters II LeetCode Solution in Python

``````class Solution:
def shiftingLetters(self, s: str, shifts: List[List[int]]) -> str:
cum_shifts = [0 for _ in range(len(s)+1)]

for st, end, d in shifts:
if d == 0:
cum_shifts[st] -= 1
cum_shifts[end+1] += 1
else:
cum_shifts[st] += 1
cum_shifts[end+1] -= 1

cum_sum = 0
for i in range(len(s)):
cum_sum += cum_shifts[i]

new_code = (((ord(s[i]) + cum_sum) - 97) % 26) + 97
s = s[:i] + chr(new_code) + s[i+1:]

return s``````
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