HDU 3887 Counting Offspring tree Array

/* Question: the relationship between 1-N and edge given on a tree. It is required to obtain the number of subnodes of each vertex that is smaller than the value of the subnode: Tree array. During dfs, sum (x-1) is obtained before entering a node x, then add operation, recursively returning node x and then sum (x-1) the difference between the two sum operations is a number smaller than x. The data volume in this question is large, and the recursion is too deep. Generally, the while + manual stack is used to simulate the recursive process, of course, c ++ can set the stack size so that the stack will not burst */# include <cstdio> # include <iostream> # include <memory. h ># include <queue> # pragma comment (linker, "/STACK: 1024000000,1024000000") using namespace std; const int MAXN = 100009; const int N = 100009; int n, root; struct Edge {int v, next;} edge [2 * MAXN + 10]; int first [MAXN], e, f [MAXN], p [MAXN], pre [MAXN]; inline void addedge (int u, int v) {edge [e]. v = v; edge [e]. next = first [u], first [u] = e ++; edge [e]. v = u; edge [e]. next = first [v], first [v] = e ++;} void init () {memset (first,-1, sizeof (first); memset (f, 0, sizeof (f); e = 0; int u, v; for (int I = 0; I <n-1; I ++) {scanf ("% d", & u, & v); addedge (u, v) ;}} int ar [N]; inline int lowb (int t) {return t & (-t) ;}void add (int I, int v) {for (; I <N; ar [I] + = v, I + = lowb (I);} in T sum (int I) {int s = 0; for (; I> 0; s + = ar [I], I-= lowb (I); return s ;} void dfs (int x, int fa) {pre[ x] = sum (x-1); for (int k = first [x]; k! =-1; k = edge [k]. next) {if (edge [k]. v! = Fa) {p [edge [k]. v] = x; add (edge [k]. v, 1); dfs (edge [k]. v, x) ;}} f [x] = sum (x-1)-pre [x];} void solve () {memset (ar, 0, sizeof (ar )); dfs (root, root); for (int I = 1; I <n; I ++) printf ("% d", f [I]); printf ("% d \ n", f [n]);} int main () {while (scanf ("% d", & n, & root ), n + root) {init (); solve ();} return 0 ;}