UVA10763ForeignExchange

//UVA10763ForeignExchange#include<cstdio>#include<cstdlib>#include<cstring>const int MAXN = 500000 + 10;void Swap(int &a, int &b) {int tmp = a;a = b;b = tmp;}int main() {int n, a[MAXN] = {0};while(scanf("%d", &n) == 1 && n) {for(int i = 0; i <= n; i++) a[i] = i;for(int i = 0; i < n; i++) {int t1, t2;scanf("%d%d", &t1, &t2);Swap(a[t1], a[t2]);}int i = 0;for(i = 0; i <= n; i++)     if(a[i] != i) break;if(i == n + 1) printf("YES\n");else printf("NO\n");}return 0;}/*101 22 13 44 3100 200200 10057 22 571 22 1101 23 45 67 89 1011 1213 1415 1617 1819 200*/