HDU 2544 最短路

標籤：

Description

就是最短路

Algorithm

Dijkstra
我就用最水的 未加最佳化的做了一下 理論時間複雜度O(V^2)
V為頂點數
後來想想光一開始賦值INF就用了V^2實在不划算
就做了個hasCost的最佳化，空間換時間，不過也沒有快多少
還是要學優先隊列的最佳化啊

Code第一版

import java.util.Arrays;import java.util.Scanner;public class Main {  public static void main(String[] args) {    Scanner cin = new Scanner(System.in);    for (;;) {      int n = cin.nextInt();      int m = cin.nextInt();      if (n == 0) break;      int[][] cost = new int[n][n];      for (int i = 0; i < n; i++) {        Arrays.fill(cost[i], Integer.MAX_VALUE / 2);        cost[i][i] = 0;      }      for (int i = 0; i < m; i++) {        int a = cin.nextInt() - 1;        int b = cin.nextInt() - 1;        int c = cin.nextInt();        cost[a][b] = c;        cost[b][a] = c;      }      int[] d = new int[n];      Arrays.fill(d, Integer.MAX_VALUE / 2);      boolean[] used = new boolean[n];      d[0] = 0;      for (;;) {        int v = -1;        for (int u = 0; u < n; u++) {          if (!used[u] && (v == -1 || d[u] < d[v])) v = u;        }        if (v == -1) break;        used[v] = true;        for (int u = 0; u < n; u++) {          d[u] = Math.min(d[u], d[v] + cost[v][u]);        }      }      System.out.println(d[n - 1]);    }  }}

第二版

import java.util.Arrays;import java.util.Scanner;public class Main {  public static void main(String[] args) {    final int INF = Integer.MAX_VALUE / 2;    Scanner cin = new Scanner(System.in);    for (;;) {      int n = cin.nextInt();      int m = cin.nextInt();      if (n == 0) break;      int[][] cost = new int[n][n];      boolean[][] hasCost = new boolean[n][n];      for (int i = 0; i < m; i++) {        int a = cin.nextInt() - 1;        int b = cin.nextInt() - 1;        int c = cin.nextInt();        cost[a][b] = c;        cost[b][a] = c;        hasCost[a][b] = true;        hasCost[b][a] = true;      }      int[] d = new int[n];      Arrays.fill(d, INF);      boolean[] used = new boolean[n];      d[0] = 0;      for (;;) {        int v = -1;        for (int u = 0; u < n; u++) {          if (!used[u] && (v == -1 || d[u] < d[v])) v = u;        }        if (v == -1) break;        used[v] = true;        for (int u = 0; u < n; u++) {          int w = d[v] + cost[v][u];          if (!hasCost[v][u]) w = INF;          d[u] = Math.min(d[u], w);        }      }      System.out.println(d[n - 1]);    }  }}

HDU 2544 最短路