c/c++语言开发共享洛谷P4719 【模板】动态dp(ddp LCT)

题意

题目链接

sol

动态dp板子题。有些细节还没搞懂，待我研究明白后再补题解。。。

#include<bits/stdc++.h> #define ll long long  using namespace std; const int maxn = 1e5 + 10, inf = int_max; template<typename a, typename b> inline bool chmax(a &x, b y) {     return x < y ? x = y, 1 : 0; } inline int read() {     char c = getchar(); int x = 0, f = 1;     while(c < '0' || c > '9') {if(c == '-') f = -1; c = getchar();}     while(c >= '0' && c <= '9') x = x * 10 + c - '0', c = getchar();     return x * f; } int n, m, a[maxn], f[maxn][2]; struct ma {     ll m[3][3];     ma() {         memset(m, -0x3f, sizeof(m));     }     ma operator * (const ma &rhs) const {         ma ans;         for(int i = 1; i <= 2; i++)             for(int j = 1; j <= 2; j++)                 for(int k = 1; k <= 2; k++)                     chmax(ans.m[i][j], m[i][k] + rhs.m[k][j]);         return ans;     } }val[maxn], sum[maxn]; vector<int> v[maxn]; int ch[maxn][2], fa[maxn]; #define ls(x) ch[x][0] #define rs(x) ch[x][1] void update(int k) {     sum[k] = val[k];     if(rs(k)) sum[k] = sum[k] * sum[rs(k)];     if(ls(k)) sum[k] = sum[ls(k)] * sum[k]; } bool ident(int x) {     return rs(fa[x]) == x; } bool isroot(int x) {     return ls(fa[x]) != x && rs(fa[x]) != x; } void connect(int x, int _fa, int tag) {     fa[x] = _fa;     ch[_fa][tag] = x; } void rotate(int x) {     int y = fa[x], r = fa[y], yson = ident(x), rson = ident(y);     int b = ch[x][yson ^ 1];     fa[x] = r;     if(!isroot(y)) connect(x, r, rson);     connect(b, y, yson);     connect(y, x, yson ^ 1);     update(y); update(x); } void splay(int x) {     for(int y = fa[x]; !isroot(x); rotate(x), y = fa[x])         if(!isroot(y))             rotate(ident(y) == ident(x) ? y : x); } void access(int x) {     for(int y = 0; x; x = fa[y = x]) {         splay(x);         if(rs(x)) {             val[x].m[1][1] += max(sum[rs(x)].m[1][1], sum[rs(x)].m[2][1]);             val[x].m[2][1] += sum[rs(x)].m[1][1];         }         if(y) {             val[x].m[1][1] -= max(sum[y].m[1][1], sum[y].m[2][1]);             val[x].m[2][1] -= sum[y].m[1][1];         }         val[x].m[1][2] = val[x].m[1][1];         rs(x) = y;         update(x);     } } int modify(int p, int v) {     access(p); splay(p);     val[p].m[2][1] -= a[p] - v;      update(p);     a[p] = v;     splay(1);     return max(sum[1].m[1][1], sum[1].m[2][1]); } void dfs(int x, int _fa) {     fa[x] = _fa;     f[x][1] = a[x];     for(auto &to : v[x]) {         if(to == _fa) continue;         dfs(to, x);         f[x][0] += max(f[to][0], f[to][1]);         f[x][1] += f[to][0];     }     val[x].m[1][1] = f[x][0]; val[x].m[1][2] = f[x][0];     val[x].m[2][1] = f[x][1]; val[x].m[2][2] = -inf;     update(x); //  sum[x] = val[x]; } int main() {     //freopen("a.in", "r", stdin);     n = read(); m = read();     for(int i = 1; i <= n; i++) a[i] = read();     for(int i = 1; i < n; i++) {         int x = read(), y = read();         v[x].push_back(y);         v[y].push_back(x);     }     dfs(1, 0);     while(m--) {         int x = read(), y = read();         printf("%dn", modify(x, y));     }     return 0; }