1471. Tree(LCA)

1471

先学习了下tarjan算法的LCA 离线算法 它是先知道询问的结点对 在遍历的时候就已经算出来了

看篇图解 讲的很清楚

 1 #include <iostream>

 2 #include<cstdio>

 3 #include<cstring>

 4 #include<algorithm>

 5 #include<stdlib.h>

 6 using namespace std;

 7 #define N 100010

 8 struct node

 9 {

10     int u,v,w,next;

11 }ed[N<<2];

12 int head[N],t,n,q,dis[N];

13 int vis[N],ans[N],qhead[N<<2];

14 int father[N],x[N],y[N];

15 void init()

16 {

17     t = 0;

18     memset(head,-1,sizeof(head));

19     memset(qhead,-1,sizeof(qhead));

20 }

21 void add(int u,int v,int w)

22 {

23     ed[t].u = u;

24     ed[t].v = v;

25     ed[t].w = w;

26     ed[t].next = head[u];

27     head[u] = t++;

28 }

29 void add1(int u,int v,int d)

30 {

31     ed[t].w = d;

32     ed[t].u = u;

33     ed[t].v = v;

34     ed[t].next = qhead[u];

35     qhead[u] = t++;

36 }

37 int find(int x)

38 {

39     if(x!=father[x])

40     father[x] = find(father[x]);

41     return father[x];

42 }

43 void tarjan(int u)

44 {

45     int i;

46     for(i = qhead[u] ; i!=-1 ; i = ed[i].next)

47     {

48         int v = ed[i].v;

49         if(vis[v])

50         ans[ed[i].w] = find(v);

51     }

52     for(i = head[u] ; i!=-1 ; i = ed[i].next)

53     {

54         int v = ed[i].v;

55         if(!vis[v])

56         {

57            vis[v] = 1;

58            dis[v] = dis[u]+ed[i].w;

59            tarjan(v);

60            father[v] = u;

61         }

62     }

63 }

64 int main()

65 {

66     int i,a,b,c;

67     init();

68     scanf("%d",&n);

69     for(i = 0; i < n ; i++)

70     father[i] = i;

71     for(i = 1 ; i < n ; i++)

72     {

73         scanf("%d%d%d",&a,&b,&c);

74         add(a,b,c);

75         add(b,a,c);

76     }

77     scanf("%d",&q);

78     for(i = 1; i <= q ; i++)

79     {

80         scanf("%d%d",&x[i],&y[i]);

81         add1(x[i],y[i],i);

82         add1(y[i],x[i],i);

83     }

84     vis[0] = 1;

85     tarjan(0);

86     for(i = 1; i <= q ; i++)

87     {

88         printf("%d\n",dis[x[i]]+dis[y[i]]-2*(dis[ans[i]]));

89     }

90     return 0;

91 }

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