OJ-Problems-Source/HDOJ/1941_autoAC.cpp

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#include<stdio.h>
#include<string.h>
#include<algorithm>
#define MAXD 50010
#define MAXM 200010
#define INF 0x3f3f3f3f
int N, M, first[MAXD], e, next[MAXM], v[MAXM], dgr[MAXD], isin[MAXD], r[MAXD];
bool cmp(const int &x, const int &y)
{
return dgr[x] < dgr[y];
}
void add(int x, int y)
{
v[e] = y;
next[e] = first[x], first[x] = e ++;
}
void init()
{
int i, x, y;
memset(first, -1, sizeof(first[0]) * (N + 1)), e = 0;
memset(dgr, 0, sizeof(dgr[0]) * (N + 1));
for(i = 0; i < M; i ++)
{
scanf("%d%d", &x, &y);
++ dgr[x], ++ dgr[y];
add(x, y), add(y, x);
}
}
void solve()
{
int i, j, x, cnt = 0, min = INF;
memset(isin, 0, sizeof(isin[0]) * (N + 1));
for(i = 1; i <= N; i ++) r[i] = i;
std::sort(r + 1, r + 1 + N, cmp);
for(i = 1; i <= N; i ++)
if(!isin[x = r[i]])
{
for(j = first[x]; j != -1; j = next[j])
-- dgr[v[j]], isin[v[j]] = 1;
}
for(i = 1; i <= N; i ++)
if(isin[x = r[i]])
++ cnt, min = std::min(min, dgr[x]);
printf("%s\n", cnt == min + 1 ? "Y" : "N");
}
int main()
{
while(scanf("%d%d", &N, &M), N)
{
if(M == 0)
{
printf("Y\n");
continue;
}
init();
solve();
}
return 0;
}