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‎src/class183/Code03_Race1.java‎

Lines changed: 261 additions & 1 deletion
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package class183;
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3-
// 边最少的权值和为k的路径，java版
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// 权值和为k的路径的最少边数，java版
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// 测试链接 : https://www.luogu.com.cn/problem/P4149
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// 提交以下的code，提交时请把类名改成"Main"，可以通过所有测试用例
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import java.io.IOException;
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import java.io.InputStream;
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import java.io.OutputStreamWriter;
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import java.io.PrintWriter;
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import java.util.Arrays;
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public class Code03_Race1 {
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public static int MAXN = 200001;
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public static int MAXK = 1000001;
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public static int INF = 1000000001;
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public static int n, k, total;
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public static int[] head = new int[MAXN];
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public static int[] nxt = new int[MAXN << 1];
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public static int[] to = new int[MAXN << 1];
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public static int[] weight = new int[MAXN << 1];
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public static int cntg;
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public static boolean[] vis = new boolean[MAXN];
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public static int[] siz = new int[MAXN];
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public static int[] maxPart = new int[MAXN];
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public static int centroid;
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public static int[] sumArr = new int[MAXN];
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public static int[] edgeArr = new int[MAXN];
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public static int cnta;
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public static int[] dp = new int[MAXK];
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// java的实现，getCentroid方法、getPath方法改成迭代才能通过，C++的实现不需要改动
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// 讲解118，讲了如何把递归函数改成迭代
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public static int[][] stack = new int[MAXN][5];
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public static int stacksize, u, f, sum, edge, e;
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public static void push(int u, int f, int sum, int edge, int e) {
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stack[stacksize][0] = u;
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stack[stacksize][1] = f;
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stack[stacksize][2] = sum;
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stack[stacksize][3] = edge;
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stack[stacksize][4] = e;
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stacksize++;
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}
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public static void pop() {
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--stacksize;
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u = stack[stacksize][0];
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f = stack[stacksize][1];
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sum = stack[stacksize][2];
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edge = stack[stacksize][3];
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e = stack[stacksize][4];
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}
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public static void addEdge(int u, int v, int w) {
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nxt[++cntg] = head[u];
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to[cntg] = v;
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weight[cntg] = w;
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head[u] = cntg;
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}
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// 找重心的递归版，java会爆栈，C++可以通过
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public static void getCentroid1(int u, int fa) {
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siz[u] = 1;
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maxPart[u] = 0;
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for (int e = head[u]; e > 0; e = nxt[e]) {
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int v = to[e];
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if (v != fa && !vis[v]) {
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getCentroid1(v, u);
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siz[u] += siz[v];
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maxPart[u] = Math.max(siz[v], maxPart[u]);
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}
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}
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maxPart[u] = Math.max(maxPart[u], total - siz[u]);
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if (centroid == 0 || maxPart[u] < maxPart[centroid]) {
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centroid = u;
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}
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}
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// 找重心的迭代版
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public static void getCentroid2(int cur, int fa) {
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stacksize = 0;
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push(cur, fa, 0, 0, -1);
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while (stacksize > 0) {
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pop();
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if (e == -1) {
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siz[u] = 1;
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maxPart[u] = 0;
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e = head[u];
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} else {
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e = nxt[e];
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}
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if (e != 0) {
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push(u, f, 0, 0, e);
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int v = to[e];
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if (v != f && !vis[v]) {
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push(to[e], u, 0, 0, -1);
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}
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} else {
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for (int ei = head[u]; ei > 0; ei = nxt[ei]) {
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int v = to[ei];
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if (v != f && !vis[v]) {
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siz[u] += siz[v];
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maxPart[u] = Math.max(siz[v], maxPart[u]);
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}
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}
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maxPart[u] = Math.max(maxPart[u], total - siz[u]);
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if (centroid == 0 || maxPart[u] < maxPart[centroid]) {
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centroid = u;
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}
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}
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}
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}
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// 收集路径的递归版，java会爆栈，C++可以通过
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public static void getPath1(int u, int fa, int sum, int edge) {
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if (sum > k) {
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return;
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}
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sumArr[++cnta] = sum;
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edgeArr[cnta] = edge;
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for (int e = head[u]; e > 0; e = nxt[e]) {
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int v = to[e];
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if (v != fa && !vis[v]) {
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getPath1(v, u, sum + weight[e], edge + 1);
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}
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}
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}
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// 收集路径的迭代版
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public static void getPath2(int cur, int fa, int psum, int pedge) {
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stacksize = 0;
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push(cur, fa, psum, pedge, -1);
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while (stacksize > 0) {
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pop();
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if (e == -1) {
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if (sum > k) {
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continue;
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}
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sumArr[++cnta] = sum;
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edgeArr[cnta] = edge;
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e = head[u];
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} else {
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e = nxt[e];
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}
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if (e != 0) {
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push(u, f, sum, edge, e);
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int v = to[e];
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if (v != f && !vis[v]) {
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push(to[e], u, sum + weight[e], edge + 1, -1);
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}
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}
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}
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}
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public static int calc(int u) {
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int ans = INF;
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cnta = 0;
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dp[0] = 0;
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for (int e = head[u]; e > 0; e = nxt[e]) {
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int v = to[e];
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if (!vis[v]) {
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int tmp = cnta;
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// getPath1(v, u, weight[e], 1);
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getPath2(v, u, weight[e], 1);
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for (int i = tmp + 1; i <= cnta; i++) {
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ans = Math.min(ans, dp[k - sumArr[i]] + edgeArr[i]);
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}
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for (int i = tmp + 1; i <= cnta; i++) {
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dp[sumArr[i]] = Math.min(dp[sumArr[i]], edgeArr[i]);
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}
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}
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}
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for (int i = 1; i <= cnta; i++) {
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dp[sumArr[i]] = INF;
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}
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return ans;
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}
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public static int compute(int u) {
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int ans = INF;
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vis[u] = true;
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ans = Math.min(ans, calc(u));
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for (int e = head[u]; e > 0; e = nxt[e]) {
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int v = to[e];
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if (!vis[v]) {
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total = siz[v];
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centroid = 0;
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// getCentroid1(v, 0);
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getCentroid2(v, 0);
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ans = Math.min(ans, compute(centroid));
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}
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}
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return ans;
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}
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public static void main(String[] args) throws Exception {
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FastReader in = new FastReader(System.in);
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PrintWriter out = new PrintWriter(new OutputStreamWriter(System.out));
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n = in.nextInt();
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k = in.nextInt();
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for (int i = 1, u, v, w; i < n; i++) {
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u = in.nextInt() + 1;
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v = in.nextInt() + 1;
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w = in.nextInt();
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addEdge(u, v, w);
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addEdge(v, u, w);
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}
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total = n;
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centroid = 0;
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// getCentroid1(1, 0);
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getCentroid2(1, 0);
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Arrays.fill(dp, INF);
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int ans = compute(centroid);
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if (ans == INF) {
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ans = -1;
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}
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out.println(ans);
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out.flush();
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out.close();
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}
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// 读写工具类
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static class FastReader {
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private final byte[] buffer = new byte[1 << 20];
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private int ptr = 0, len = 0;
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private final InputStream in;
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FastReader(InputStream in) {
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this.in = in;
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}
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private int readByte() throws IOException {
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if (ptr >= len) {
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len = in.read(buffer);
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ptr = 0;
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if (len <= 0)
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return -1;
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}
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return buffer[ptr++];
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}
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int nextInt() throws IOException {
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int c;
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do {
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c = readByte();
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} while (c <= ' ' && c != -1);
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boolean neg = false;
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if (c == '-') {
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neg = true;
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c = readByte();
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}
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int val = 0;
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while (c > ' ' && c != -1) {
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val = val * 10 + (c - '0');
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c = readByte();
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}
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return neg ? -val : val;
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}
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}
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}

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