848.Shifting Letters——weekly contest 87

848. Shifting Letters

题目链接：https://leetcode.com/problems/shifting-letters/description/

思路：O（N^2）复杂度过不了；先处理shifts, 从尾到头执行shifts[i] = sum(shifts[i+1]+...+shifts[n-1])。

注意点：会爆int,及时取余或用longlong。

 1 string shiftingLetters(string S, vector<int>& shifts) {
 2         int n = S.size();
 3         for(int i = n - 2; i >= 0 ; i--){
 4             shifts[i] += shifts[i+1];
 5             shifts[i] = shifts[i]%26;
 6         }
 7         for(int i = 0; i < n; i++){
 8             S[i] = (S[i]-'a'+shifts[i])%26 + 'a';
 9         }
10         return S;
11     }