BZOJ1864 [Zjoi2006]三色二叉树

简单地树形DP

我们用f，g表示最大、最小值，0,1,2表示颜色然后直接推

递推公式请见程序233

/**************************************************************
    Problem: 1864
    User: rausen
    Language: C++
    Result: Accepted
    Time:24 ms
    Memory:19244 kb
****************************************************************/
 
#include <cstdio>
#include <algorithm>
  
#define Rep(i, n) for (i = 0; i < n; ++i)
using namespace std;
const int inf = (int) 1e9;
const int N = 500005;
  
int cnt, s[N][3], f[N][3], g[N][3];
  
void dfs(int p) {
    int i, j, k;
    s[p][0] = getchar() - '0';
    if (!s[p][0]) {
        f[p][0] = g[p][0] = 1;
        return;
    }
    for (i = 1; i <= s[p][0]; ++i) {
        s[p][i] = ++cnt;
        dfs(cnt);
    }
    g[p][0] = g[p][1] = g[p][2] = inf;
    if (s[p][0] == 1) {
        Rep(i, 3) Rep(j, 3)
            if (i != j)
                f[p][i] = max(f[p][i], f[s[p][1]][j] + !i),
                g[p][i] = min(g[p][i], g[s[p][1]][j] + !i);
    } else {
        Rep(i, 3) Rep(j, 3) Rep(k, 3)
            if (i != j && j != k && i != k)
                f[p][i] = max(f[p][i], f[s[p][1]][j] + f[s[p][2]][k] + !i),
                g[p][i] = min(g[p][i], g[s[p][1]][j] + g[s[p][2]][k] + !i);
    }
}
  
int main() {
    dfs(cnt = 1);
    printf("%d %d
", max(max(f[1][0], f[1][1]), f[1][2]), min(min(g[1][0], g[1][1]), g[1][2]));
    return 0;
}