题意:一个树,a b c 代表a--b边的权值为c。CHANGE x y 把输入的第x条边的权值改为y,QUERY x y 查询x--y路径上边的权值的最大值。
第一次写树链剖分,其实树链剖分只能说是一种思想。树链剖分 就是 先选择从根节点到叶子节点的最长的路径的权值对应到线段树上,然后从一个子树的根节点到叶子的最长路径的权值对应到线段树上这样直到把所有的点都处理了,然后就是线段树区间查询最值了。
具体可以看这个博客。http://blog.sina.com.cn/s/blog_6974c8b20100zc61.html
1 #include <cstdio> 2 #include <cstdlib> 3 #include <iostream> 4 #include <cstring> 5 #include <algorithm> 6 using namespace std; 7 typedef unsigned long long ull; 8 typedef long long ll; 9 const int inf = 0x3f3f3f3f; 10 const double eps = 1e-8; 11 const int maxn = 1e4+10; 12 int top[maxn],fa[maxn],son[maxn],dep[maxn],siz[maxn],seg_tree[maxn<<2],head[maxn],pos[maxn]; 13 int edge,tot; 14 struct 15 { 16 int to,next; 17 }e[maxn<<1]; 18 void add(int x,int y) 19 { 20 e[edge].to = y; 21 e[edge].next = head[x]; 22 head[x] = edge++; 23 } 24 25 void dfs(int r) 26 { 27 siz[r] = 1; 28 son[r] = 0; 29 for (int i = head[r]; i > 0; i = e[i].next) 30 if (fa[r] != e[i].to) 31 { 32 dep[e[i].to] = dep[r] + 1; 33 fa[e[i].to] = r; 34 dfs(e[i].to); 35 if (siz[e[i].to] > siz[son[r]]) 36 son[r] = e[i].to; 37 siz[r] += siz[e[i].to]; 38 } 39 } 40 41 void build(int r,int f) 42 { 43 pos[r] = tot++; 44 top[r] = f; 45 if (son[r] > 0) 46 build(son[r],top[r]); 47 for (int i = head[r]; i > 0; i = e[i].next) 48 { 49 if (fa[r] != e[i].to && son[r] != e[i].to) 50 build(e[i].to,e[i].to); 51 } 52 } 53 54 void update(int l,int r,int o,int x,int v) 55 { 56 if (l == r) 57 { 58 seg_tree[o] = v; 59 return; 60 } 61 int mid = (l + r) >> 1; 62 if (x <= mid) 63 update(l,mid,o<<1,x,v); 64 if (x > mid) 65 update(mid+1,r,o<<1|1,x,v); 66 seg_tree[o] = max(seg_tree[o<<1],seg_tree[o<<1|1]); 67 } 68 69 int query(int l,int r,int o,int ua,int ub) 70 { 71 if (ua <= l && ub >= r) 72 return seg_tree[o]; 73 int mid = (l + r) >> 1; 74 int t1,t2; 75 t1 = t2 = 0; 76 if (ua <= mid) 77 t1 = query(l,mid,o<<1,ua,ub); 78 if (ub > mid) 79 t2 = query(mid+1,r,o<<1|1,ua,ub); 80 return max(t1,t2); 81 } 82 83 int get_max(int ua,int ub) 84 { 85 int f1 = top[ua]; 86 int f2 = top[ub]; 87 int tmp = 0; 88 while (f1 != f2) 89 { 90 if (dep[f1] < dep[f2]) 91 swap(f1,f2),swap(ua,ub); 92 tmp = max(tmp,query(1,tot,1,pos[f1],pos[ua])); 93 ua = fa[f1],f1 = top[ua]; 94 } 95 if (ua == ub) 96 return tmp; 97 if (dep[ua] > dep[ub]) 98 swap(ua,ub); 99 tmp = max(tmp,query(1,tot,1,pos[son[ua]],pos[ub])); 100 return tmp; 101 } 102 103 int d[maxn][3]; 104 void init() 105 { 106 int n; 107 scanf ("%d",&n); 108 memset(dep,0,sizeof(dep)); 109 memset(son,0,sizeof(son)); 110 memset(head,0,sizeof(head)); 111 memset(fa,0,sizeof(fa)); 112 memset(top,0,sizeof(top)); 113 int root = (n+1)>>1; 114 fa[root] = dep[root] =0; 115 tot = edge = 1; 116 int a,b,c; 117 for (int i = 1; i < n; i++) 118 { 119 scanf ("%d%d%d",&a,&b,&c); 120 add(a,b),add(b,a); 121 d[i][0] = a,d[i][1] = b,d[i][2] = c; 122 } 123 dfs(root); 124 build(root,root); 125 tot--; 126 for (int i = 1; i < n; i++) 127 { 128 if (dep[d[i][0]] < dep[d[i][1]]) 129 swap(d[i][1],d[i][0]); 130 update(1,tot,1,pos[d[i][0]],d[i][2]); 131 } 132 133 } 134 int main(void) 135 { 136 #ifndef ONLINE_JUDGE 137 freopen("in.txt","r",stdin); 138 #endif // ONLINE_JUDGE 139 int t; 140 scanf ("%d",&t); 141 while (t--) 142 { 143 init(); 144 char op[10]; 145 while (scanf ("%s",op),op[0] != ‘D‘) 146 { 147 int x,y; 148 scanf ("%d%d",&x,&y); 149 if (op[0] == ‘C‘) 150 update(1,tot,1,pos[d[x][0]],y); 151 if (op[0] == ‘Q‘) 152 printf("%d\n",get_max(x,y)); 153 } 154 } 155 return 0; 156 }
时间: 2024-10-06 04:32:48