848.Shifting Letters

Tags: Medium String

Links: https://leetcode.com/problems/shifting-letters/

---

We have a string S of lowercase letters, and an integer array shifts.

Call the shift of a letter, the next letter in the alphabet, (wrapping around so that 'z' becomes 'a').

For example, shift('a') = 'b', shift('t') = 'u', and shift('z') = 'a'.

Now for each shifts[i] = x, we want to shift the first i+1 letters of S, x times.

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

Example 1:

Input: S = "abc", shifts = [3,5,9]
Output: "rpl"
Explanation: 
We start with "abc".
After shifting the first 1 letters of S by 3, we have "dbc".
After shifting the first 2 letters of S by 5, we have "igc".
After shifting the first 3 letters of S by 9, we have "rpl", the answer.

Note:

1. 1 <= S.length = shifts.length <= 20000
2. 0 <= shifts[i] <= 10 ^ 9

---

class Solution {
public:
    string shiftingLetters(string S, vector<int>& shifts) {
        std::ios_base::sync_with_stdio(false);
        cin.tie(NULL);
        cout.tie(NULL);

        int n = shifts.size();
        vector<int> suffixSum(n, 0);
        suffixSum[n - 1] = shifts[n - 1] % 26;
        for (int i = n - 2; i >= 0; --i) {
            suffixSum[i] = (suffixSum[i + 1] + shifts[i]) % 26;
        }

        for (int i = 0; i < n; ++i) {
            S[i] = 'a' + (S[i] - 'a' + suffixSum[i]) % 26;
        }

        return S;
    }
};

后缀和计算移位。