C. Uncle Bogdan and Country Happiness solution

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C. Uncle Bogdan and Country Happinesstime limit per test 2 secondsmemory limit per test 256 megabytesinput standard inputoutput standard outputUncle Bogdan is in captain Flint‘s crew for a long time and sometimes gets nostalgic for his homeland. Today he told you how his country introduced a happiness index.
There are  nn  cities and  n− 1n− 1  undirected roads connecting pairs of cities. Citizens of any city can reach any other city traveling by these roads. Cities are numbered from  11  to  nn  and the city  11  is a capital. In other words, the country has a tree structure.
There are  mm  citizens living in the country. A  pipi  people live in the  ii-th city but all of them are working in the capital. At evening all citizens return to their home cities using the shortest paths.
Every person has its own mood: somebody leaves his workplace in good mood but somebody are already in bad mood. Moreover any person can ruin his mood on the way to the hometown.  If person is in bad mood he won‘t improve it.
Happiness detectors are installed in each city to monitor the happiness of  each  person who visits the city. The detector in the  ii-th city calculates a happiness index  hihi  as the number of people in good mood minus the number of people in bad mood. Let‘s say for the simplicity that  mood of a person doesn‘t change inside the city.
Happiness detector is still in development, so there is a probability of a mistake in judging a person‘s happiness. One late evening, when all citizens successfully returned home, the government asked uncle Bogdan (the best programmer of the country) to check the correctness of the collected happiness indexes.
【C. Uncle Bogdan and Country Happiness solution】Uncle Bogdan successfully solved the problem. Can you do the same?
More formally,  You need to check: "Is it possible that, after all people return home, for each city  ii  the happiness index will be equal exactly to  hihi".
InputThe first line contains a single integer  tt  (1≤ t≤ 100001≤ t≤ 10000)  — the number of test cases.
The first line of each test case contains two integers  nn  and  mm  (1≤ n≤ 1051≤ n≤ 105;   0≤ m≤ 1090≤ m≤ 109)  — the number of cities and citizens.
The second line of each test case contains  nn  integers  p1,p2,… ,pnp1,p2,… ,pn  (0≤ pi≤ m0≤ pi≤ m;   p1+p2+… +pn=mp1+p2+… +pn=m), where  pipi  is the number of people living in the  ii-th city.
The third line contains  nn  integers  h1,h2,… ,hnh1,h2,… ,hn  (− 109≤ hi≤ 109− 109≤ hi≤ 109), where  hihi  is the calculated happiness index of the  ii-th city.
Next  n− 1n− 1  lines contain description of the roads, one per line. Each line contains two integers  xixi  and  yiyi  (1≤ xi,yi≤ n1≤ xi,yi≤ n;   xi≠ yixi≠ yi), where  xixi  and  yiyi  are cities connected by the  ii-th road.
It‘s guaranteed that the sum of  nn  from all test cases doesn‘t exceed  2⋅ 1052⋅ 105.
OutputFor each test case, print  YES, if the collected data is correct, or  NO  — otherwise. You can print characters in  YES  or  NO  in any case.
Examplesinput Copy

2 7 4 1 0 1 1 0 1 0 4 0 0 -1 0 -1 0 1 2 1 3 1 4 3 5 3 6 3 7 5 11 1 2 5 2 1 -11 -2 -6 -2 -1 1 2 1 3 1 4 3 5

output Copy
YES YES

input Copy
2 4 4 1 1 1 1 4 1 -3 -1 1 2 1 3 1 4 3 13 3 3 7 13 1 4 1 2 1 3

output Copy
NO NO
solution:

#include< iostream> #include< vector> using namespace std; const int N = 1e5+5; vector< int> buf[N]; int a[N],p[N],h[N],g[N]; bool flag = true; void dfs(int v, int ancestor = -1) { a[v] = p[v]; int sum = 0,to,i; for(i=0; i< buf[v].size(); i++){ to=buf[v][i]; if(to == ancestor) continue; dfs(to, v); a[v] += a[to]; sum += g[to]; //统计now节点为根的子树的总人数 } g[v] = (a[v]+h[v])/2; if((a[v]+h[v])%2 != 0||g[v] < 0 || g[v] > a[v]||sum > g[v]) flag = false; /*1.说明不是整数 2.说明快乐人数比总人数还多 3.说明经过now城市后的快乐人数竟然比走的更远的城市的快乐人数更少*/ } int main(int argc, const char** argv) { ios::sync_with_stdio(false); cin.tie(); int t; cin> > t; while(t--){ int n,m; cin> > n> > m; for(int i = 1; i < = n; ++i) cin> > p[i]; for(int i = 1; i < = n; ++i) cin> > h[i]; for(int i = 0; i < n-1; ++i){ int a,b; cin> > a> > b; buf[a].push_back(b); buf[b].push_back(a); } dfs(1); if (flag) cout < < "YES" < < endl; else cout < < "NO" < < endl; flag = true; for(int i = 1; i < =n; ++i) buf[i].clear(); } return 0; }



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