ALGO-4 结点选择 — 树型动态规划（java再优化版）

ALGO—4 结点选择
上篇的题解在最后提到，java的解法在蓝桥OJ上判为运行超时，改为C++后AC了。





在深度查阅了更多java的特性，并且试图用更java风格的算法进行优化后。最终用java也AC了。



其实主要处理的是java的输入流的速率问题。

以下附上两种优化方式的代码：（java再优化版）
第一种优化方式：import java.io.*;
import java.util.*;

public class Main {
final static int MAX = 100010;
int edgecount;
int tree[] = new int[MAX];
int dp[][] = new int[MAX][2];
int visit[] = new int[MAX * 2];
boolean visited[] = new boolean[MAX];

class Edge {
int start, end, next;
Edge(int s, int e, int n) {
start = s;
end = e;
next = n;
}
}
Edge edge[] = new Edge[MAX * 2];

void add(int start, int end) {
edge[edgecount] = new Edge(start, end, tree[start]);
tree[start] = edgecount++;
}

void dfs(int x, int x_father) {
Arrays.fill(visited, false);
int temp = 0;
visited[x] = true;
visit[temp++] = x;
while (temp > 0) {
x = visit[temp - 1];
boolean edgevisited = false;
for (int i = tree[x]; i + 1 != 0; i = edge[i].next) {
int end = edge[i].end;
if (visited[end])
continue;
edgevisited = true;
visit[temp++] = end;
visited[end] = true;
}
if (edgevisited)
continue;
--temp;
for (int i = tree[x]; i + 1 != 0; i = edge[i].next) {
int x_son = edge[i].end;
dp[x_son][0] += Math.max(dp[x][0], dp[x][1]);
dp[x_son][1] += dp[x][0];

}
}
}

void run() throws IOException {
int n = cin.nextInt();
for (int i = 1; i <= n; ++i)
dp[i][1] = cin.nextInt();
Arrays.fill(tree, -1);
for (int i = 1; i < n; ++i) {
int x = cin.nextInt();
int y = cin.nextInt();
add(x, y);
add(y, x);
}
dfs(1, 0);
int ans = Math.max(dp[1][0], dp[1][1]);
out.println(ans);
out.close();
}

public static void main(String[] args) throws IOException {
new Main().run();
}

Main() {
cin = new InputReader(System.in);
out = new PrintWriter(System.out);
}

InputReader cin;
PrintWriter out;

class InputReader {
InputReader(InputStream in) {
reader = new BufferedReader(new InputStreamReader(in));
tokenizer = new StringTokenizer("");
}

private String next() throws IOException {
while (!tokenizer.hasMoreTokens()) {
tokenizer = new StringTokenizer(reader.readLine());
}
return tokenizer.nextToken();
}

public Integer nextInt() throws IOException {
return Integer.parseInt(next());
}

private BufferedReader reader;
private StringTokenizer tokenizer;
}
}

第二种优化方式：import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.util.Arrays;
import java.util.StringTokenizer;

class Reader {
static BufferedReader reader;
static StringTokenizer tokenizer;

static void init(InputStream input) {
reader = new BufferedReader(new InputStreamReader(input));
tokenizer = new StringTokenizer("");
}

static String next() throws IOException {
while (!tokenizer.hasMoreTokens()) {
tokenizer = new StringTokenizer(reader.readLine());
}
return tokenizer.nextToken();
}

static int nextInt() throws IOException {
return Integer.parseInt(next());
}

static double nextDouble() throws IOException {
return Double.parseDouble(next());
}
}

public class Main {

final static int MAX = 100010;
static int edgecount;
static int tree[] = new int[MAX];
static int dp[][] = new int[MAX][2];
static int visit[] = new int[MAX * 2];
static boolean visited[] = new boolean[MAX];

static class Edge {
int start, end, next;
Edge(int s, int e, int n) {
start = s;
end = e;
next = n;
}
}
static Edge edge[] = new Edge[MAX * 2];

static void add(int start, int end) {
edge[edgecount] = new Edge(start, end, tree[start]);
tree[start] = edgecount++;
}

static void dfs(int x, int x_father) {
Arrays.fill(visited, false);
int temp = 0;
visited[x] = true;
visit[temp++] = x;
while (temp > 0) {
x = visit[temp - 1];
boolean edgevisited = false;
for (int i = tree[x]; i + 1 != 0; i = edge[i].next) {
int end = edge[i].end;
if (visited[end])
continue;
edgevisited = true;
visit[temp++] = end;
visited[end] = true;
}
if (edgevisited)
continue;
--temp;
for (int i = tree[x]; i + 1 != 0; i = edge[i].next) {
int x_son = edge[i].end;
dp[x_son][0] += Math.max(dp[x][0], dp[x][1]);
dp[x_son][1] += dp[x][0];

}
}
}

public static void main(String[] args) throws IOException {
Reader.init(System.in);
int n = Reader.nextInt();
for (int i = 1; i <= n; ++i)
dp[i][1] = Reader.nextInt();
Arrays.fill(tree, -1);
for (int i = 1; i < n; ++i) {
int x = Reader.nextInt();
int y = Reader.nextInt();
add(x, y);
add(y, x);
}
dfs(1, 0);
int ans = Math.max(dp[1][0], dp[1][1]);
System.out.println(ans);
}
}

其中关于String Tokenizer类的介绍详见博文：http://blog.csdn.net/sobermineded/article/details/79299113