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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