Mahmoud and Ehab live in a country with n cities numbered from 1 to n and connected by n?-?1 undirected roads. It‘s guaranteed that you can reach any city from any other using these roads. Each city has a number ai attached to it.
We define the distance from city x to city y as the xor of numbers attached to the cities on the path from x to y (including both x and y). In other words if values attached to the cities on the path from x to y form an array p of length l then the distance between them is , where
is bitwise xor operation.
Mahmoud and Ehab want to choose two cities and make a journey from one to another. The index of the start city is always less than or equal to the index of the finish city (they may start and finish in the same city and in this case the distance equals the number attached to that city). They can‘t determine the two cities so they try every city as a start and every city with greater index as a finish. They want to know the total distance between all pairs of cities.
Input
The first line contains integer n (1?≤?n?≤?105) — the number of cities in Mahmoud and Ehab‘s country.
Then the second line contains n integers a1,?a2,?...,?an (0?≤?ai?≤?106) which represent the numbers attached to the cities. Integer ai is attached to the city i.
Each of the next n??-??1 lines contains two integers u and v (1??≤??u,??v??≤??n, u??≠??v), denoting that there is an undirected road between cities u and v. It‘s guaranteed that you can reach any city from any other using these roads.
Output
Output one number denoting the total distance between all pairs of cities.
Example
3
1 2 3
1 2
2 3
10
5
1 2 3 4 5
1 2
2 3
3 4
3 5
52
5
10 9 8 7 6
1 2
2 3
3 4
3 5
131
Note
A bitwise xor takes two bit integers of equal length and performs the logical xor operation on each pair of corresponding bits. The result in each position is 1 if only the first bit is 1 or only the second bit is 1, but will be 0 if both are 0 or both are 1. You can read more about bitwise xor operation here: https://en.wikipedia.org/wiki/Bitwise_operation#XOR.
In the first sample the available paths are:
1 #include<bits/stdc++.h> 2 #include <iostream> 3 using namespace std; 4 typedef long long ll; 5 typedef unsigned long long ull; 6 const int MAX=1e5+5; 7 vector <int> t[MAX]; 8 int n; 9 int a[MAX]; 10 ll an=0; 11 int num[MAX][2]; 12 void dfs(int now,int fa,int wei) 13 { 14 int tem=(a[now]>>wei)&1; 15 num[now][tem]=1;num[now][tem^1]=0; 16 ll re=0; 17 for(int i=0;i<t[now].size();i++) 18 { 19 int s=t[now][i]; 20 if(s==fa) 21 continue; 22 dfs(s,now,wei); 23 re+=num[now][0]*num[s][1]+num[now][1]*num[s][0]; 24 num[now][tem^0]+=num[s][0]; 25 num[now][tem^1]+=num[s][1]; 26 } 27 an+=(re<<wei); 28 } 29 int main() 30 { 31 scanf("%d",&n); 32 int i; 33 for(i=1;i<=n;i++) 34 { 35 scanf("%d",&a[i]); 36 an+=a[i]; 37 } 38 int x,y; 39 for(i=0;i<n-1;i++) 40 { 41 scanf("%d %d",&x,&y); 42 t[x].push_back(y); 43 t[y].push_back(x); 44 } 45 for(i=0;i<=30;i++) 46 dfs(1,0,i); 47 printf("%I64d\n",an); 48 }
Codeforces Round #396 (Div. 2) E题Mahmoud and a xor trip（树状dp）解题报告
原文：http://www.cnblogs.com/quintessence/p/6384651.html