codeforces 902b 根树的性质与染色

You are given a rooted tree with n vertices. The vertices are numbered from 1 to n, the root is the vertex number 1.

Each vertex has a color, let's denote the color of vertex v by c_v. Initially c_v = 0.

You have to color the tree into the given colors using the smallest possible number of steps. On each step you can choose a vertex v and a color x, and then color all vectices in the subtree of v (including v itself) in color x. In other words, for every vertex u, such that the path from root to u passes through v, set c_u = x.

It is guaranteed that you have to color each vertex in a color different from 0.

You can learn what a rooted tree is using the link: https://en.wikipedia.org/wiki/Tree_(graph_theory).

居然只要比较父子节点的颜色，厉害

思维题，

不要被bfs迷惑了

#include <iostream>
#include <cstdio>
using namespace std;
int father[10016],color[10016];
int main(void)
{
    int n;
    scanf("%d",&n);
    for(int i=2;i<=n;i++)
        scanf("%d",&father[i]);
    for(int i=1;i<=n;i++)
        scanf("%d",&color[i]);
    int ans=1;
    for(int i=2;i<=n;i++)
        if(color[i]!=color[father[i]])
            ans++;
        printf("%d\n",ans );
    return 0;
}