CF EDU 112 D - Say No to Palindromes
阿新 • • 發佈:2022-05-12
D - Say No to Palindromes
列舉
可觀察到只有類似 abcabcabcabc..., bacbacbac... 等 abc 三個字母都迴圈出現才滿足要求
可記錄 \(cnt[i][j][k]\),前 \(i\) 箇中 \(a, b, c\) 分別在 模 \(3\) 餘 \(0,1,2\) 的個數
因此列舉 abc 的 6 種排列,用字首和求最小改動次數即可
#include <iostream> #include <cstring> #include <algorithm> #include <vector> #include <cmath> using namespace std; typedef long long ll; const int N = 2e5 + 10; string s; int cnt[N][3][3];//cnt[i][j][k]為前i個字母中(a, b, c)分別在(0, 1, 2)三個位置的個數 int n, m; int l, r; int solve(int a, int b, int c) { int cnt_a = cnt[r][a][0] - cnt[l-1][a][0]; int cnt_b = cnt[r][b][1] - cnt[l-1][b][1]; int cnt_c = cnt[r][c][2] - cnt[l-1][c][2]; return r - l + 1 - cnt_a - cnt_b - cnt_c; } int main() { ios::sync_with_stdio(false), cin.tie(0), cout.tie(0); cin >> n >> m; cin >> s; s = " " + s; for (int i = 1; i < s.size(); i++) { for (int j = 0; j < 3; j++) for (int k = 0; k < 3; k++) cnt[i][j][k] = cnt[i-1][j][k]; char ch = s[i]; int t = i % 3; if (ch == 'a') cnt[i][0][t]++; else if (ch == 'b') cnt[i][1][t]++; else cnt[i][2][t]++; } while(m--) { cin >> l >> r; int ans = 1e9; ans = min(ans, solve(0, 1, 2)); ans = min(ans, solve(0, 2, 1)); ans = min(ans, solve(1, 0, 2)); ans = min(ans, solve(1, 2, 0)); ans = min(ans, solve(2, 0, 1)); ans = min(ans, solve(2, 1, 0)); cout << ans << endl; } return 0; }