大意略。
思路:catalan数,好险啊,差点TLE了。
#include <iostream> #include <cstdlib> #include <cstdio> #include <cstring> #include <string> using namespace std; const int MAXN = 1100; int n; struct bign { int len, s[MAXN]; bign () { memset(s, 0, sizeof(s)); len = 1; } bign (int num) {*this = num;} bign (const char *num) { *this = num;} bign operator = (const char *num) { len = strlen(num); for(int i = 0; i < len; i++) s[i] = num[len-i-1] - '0'; return *this; } bign operator = (int num) { char s[MAXN]; sprintf(s, "%d", num); *this = s; return *this; } bign operator +(const bign &b) const { bign c; c.len = 0; for(int i = 0, g = 0; g || i < max(len, b.len); i++) { int x = g; if(i < len) x += s[i]; if(i < b.len) x += b.s[i]; c.s[c.len++] = x%10; g = x / 10; } return c; } bign operator += (const bign &b) { *this = *this + b; return *this; } void clean() { while(len > 1 && !s[len-1]) len--; } bign operator * (const bign &b) const { bign c; c.len = len + b.len; for(int i = 0; i < len; i++) { for(int j = 0; j < b.len; j++) { c.s[i+j] += s[i] * b.s[j]; } } for(int i = 0; i < c.len; i++) { c.s[i+1] += c.s[i] / 10; c.s[i] %= 10; } c.clean(); return c; } bign operator - (const bign &b) { bign c; c.len = 0; for(int i = 0, g = 0; i < len; i++) { int x = s[i] - g; if(i < b.len) x -= b.s[i]; if(x >= 0) g = 0; else { g = 1; x += 10; } c.s[c.len++] = x; } c.clean(); return c; } bign operator / (const bign &b) { bign c, f = 0; for(int i = len-1; i >= 0; i--) { f = f*10; f.s[0] = s[i]; while(f >= b) { f = f - b; c.s[i]++; } } c.len = len; c.clean(); return c; } bool operator < (const bign &b) const { if(len != b.len) return len < b.len; for(int i = len-1; i >= 0; i--) { if(s[i] != b.s[i]) return s[i] < b.s[i]; } return false; } bool operator >= (const bign &b) const { return !(*this < b); } string str() const { string res = ""; for(int i = 0; i < len; i++) res = char(s[i]+'0') + res; if(res == "") res = "0"; return res; } }; bign catalan[1500]; ostream& operator << (ostream &out, bign &x) { out << x.str(); return out; } void init() { catalan[1] = 1; for(int i = 2; i <= 1499; i++) { catalan[i] = catalan[i-1] * (4*i-2) / (i+1); } } int main() { init(); while(~scanf("%d", &n)) { cout<<catalan[n]<<endl; } return 0; }