#include <bits/stdc++.h> using namespace std; #define loop(i, a, b) for(int i = a; i <= b; i++) #define loop_rev(i, a, b) for(int i = a; i >= b; i--) #define all(x) x.begin(), x.end() #define sz(x) int(x.size()) #define pb push_back using ll = long long; void solve(); vector<int> s; int n, q; vector<vector<vector<vector<int>>>> dp; int maxi = 0; signed main() { cin.tie(0)->sync_with_stdio(0); string str; cin >> n >> q >> str; dp.resize(n + 1, vector(n + 1, vector(6, vector(6, int(0))))); s.resize(n + 1); multiset<int> colors; loop(i, 1, n) { s[i] = (str[i - 1] - 'a'); colors.insert(s[i]); } maxi = *prev(colors.end()); solve(); loop(qi, 1, q) { int i; char c; cin >> i >> c; colors.erase(colors.find(s[i])); s[i] = (c - 'a'); colors.insert(s[i]); maxi = *prev(colors.end()); solve(); } } constexpr int MOD = 998'244'353; ll add(ll a, ll b) { return (a + b >= MOD ? a + b - MOD : a + b); } ll sub(ll a, ll b) { return (a - b < 0 ? a - b + MOD : a - b); } ll mul(ll a, ll b) { return (a * b) % MOD; } vector<vector<int>> nast, pop; int rec(int a, int b, int c1, int c2) { int& res = dp[a][b][c1][c2]; if(res) return (res - 1); if(a == b) { return (res = 2) - 1; } int lim1 = nast[c1][a]; int lim2 = pop[c2][b]; res = 1; if((!lim1 || lim1 >= b) && lim2 <= a) { ++res; } loop(nc1, 0, maxi) { int x = nast[nc1][a]; if(!x || (lim1 && x > lim1)) continue; loop(nc2, 0, maxi) { int y = pop[nc2][b]; if(x > y || (lim2 && y < lim2)) continue; int new_add = rec(x, y, nc1, nc2); res = add(res, new_add); } } return (res - 1); } void solve() { nast.resize(6, vector<int>(n + 2)); pop.resize(6, vector<int>(n + 2)); loop(i, 1, n) { loop(j, i, n) { loop(c1, 0, maxi) { loop(c2, 0, maxi) { dp[i][j][c1][c2] = 0; } } } } loop(i, 1, n) { loop(c, 0, maxi) { if(s[i] == c) { pop[c][i + 1] = i; } else { pop[c][i + 1] = pop[c][i]; } } } loop_rev(i, n, 1) { loop(c, 0, maxi) { if(s[i] == c) { nast[c][i - 1] = i; } else { nast[c][i - 1] = nast[c][i]; } } } int res = 0; loop(c1, 0, maxi) { int a = nast[c1][0]; if(!a) continue; loop(c2, 0, maxi) { int b = pop[c2][n + 1]; if(a > b) continue; int new_add = rec(a, b, c1, c2); res = add(res, new_add); } } vector<int> cnt_arr(6); int cnt = 1; loop(i, 1, n) { int old_cnt = cnt; cnt = sub(mul(cnt, 2), cnt_arr[s[i]]); cnt_arr[s[i]] = old_cnt; } cout << sub(cnt, add(res, 1)) << '\n'; }
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 | #include <bits/stdc++.h> using namespace std; #define loop(i, a, b) for(int i = a; i <= b; i++) #define loop_rev(i, a, b) for(int i = a; i >= b; i--) #define all(x) x.begin(), x.end() #define sz(x) int(x.size()) #define pb push_back using ll = long long; void solve(); vector<int> s; int n, q; vector<vector<vector<vector<int>>>> dp; int maxi = 0; signed main() { cin.tie(0)->sync_with_stdio(0); string str; cin >> n >> q >> str; dp.resize(n + 1, vector(n + 1, vector(6, vector(6, int(0))))); s.resize(n + 1); multiset<int> colors; loop(i, 1, n) { s[i] = (str[i - 1] - 'a'); colors.insert(s[i]); } maxi = *prev(colors.end()); solve(); loop(qi, 1, q) { int i; char c; cin >> i >> c; colors.erase(colors.find(s[i])); s[i] = (c - 'a'); colors.insert(s[i]); maxi = *prev(colors.end()); solve(); } } constexpr int MOD = 998'244'353; ll add(ll a, ll b) { return (a + b >= MOD ? a + b - MOD : a + b); } ll sub(ll a, ll b) { return (a - b < 0 ? a - b + MOD : a - b); } ll mul(ll a, ll b) { return (a * b) % MOD; } vector<vector<int>> nast, pop; int rec(int a, int b, int c1, int c2) { int& res = dp[a][b][c1][c2]; if(res) return (res - 1); if(a == b) { return (res = 2) - 1; } int lim1 = nast[c1][a]; int lim2 = pop[c2][b]; res = 1; if((!lim1 || lim1 >= b) && lim2 <= a) { ++res; } loop(nc1, 0, maxi) { int x = nast[nc1][a]; if(!x || (lim1 && x > lim1)) continue; loop(nc2, 0, maxi) { int y = pop[nc2][b]; if(x > y || (lim2 && y < lim2)) continue; int new_add = rec(x, y, nc1, nc2); res = add(res, new_add); } } return (res - 1); } void solve() { nast.resize(6, vector<int>(n + 2)); pop.resize(6, vector<int>(n + 2)); loop(i, 1, n) { loop(j, i, n) { loop(c1, 0, maxi) { loop(c2, 0, maxi) { dp[i][j][c1][c2] = 0; } } } } loop(i, 1, n) { loop(c, 0, maxi) { if(s[i] == c) { pop[c][i + 1] = i; } else { pop[c][i + 1] = pop[c][i]; } } } loop_rev(i, n, 1) { loop(c, 0, maxi) { if(s[i] == c) { nast[c][i - 1] = i; } else { nast[c][i - 1] = nast[c][i]; } } } int res = 0; loop(c1, 0, maxi) { int a = nast[c1][0]; if(!a) continue; loop(c2, 0, maxi) { int b = pop[c2][n + 1]; if(a > b) continue; int new_add = rec(a, b, c1, c2); res = add(res, new_add); } } vector<int> cnt_arr(6); int cnt = 1; loop(i, 1, n) { int old_cnt = cnt; cnt = sub(mul(cnt, 2), cnt_arr[s[i]]); cnt_arr[s[i]] = old_cnt; } cout << sub(cnt, add(res, 1)) << '\n'; } |