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| #include <bits/stdc++.h>
using namespace std;
typedef pair<int,int> pr;
const int N = 1e5 + 66, M = 5e5 + 66;
inline int read()
{
int s(0), w(1);
char ch = getchar();
while (ch < '0' || ch > '9') {if (ch == '-') w = -1; ch = getchar();}
while (ch >= '0' && ch <= '9') s = s * 10 + ch - '0', ch = getchar();
return s * w;
}
inline void put(int x)
{
if (! x) putchar('0');
if (x < 0) putchar('-'), x = -x;
int num(0); char c[66];
while (x) c[++ num] = x % 10 + 48, x /= 10;
while (num) putchar(c[num --]);
return (void)(putchar('\n'));
}
map<pr, bool>existed;
int ver[M], nex[M], head[N], cnt;
inline void add_edge(int x, int y)
{
ver[++ cnt] = y;
nex[cnt] = head[x];
return (void)(head[x] = cnt);
}
int n, m, top, tot, num, res;
int minv[N], maxv[N];
int dfn[N], low[N], sta[N], in[N], tar[N], v[N];
inline void tarjan(int x)
{
dfn[x] = low[x] = ++ tot, in[x] = 1, sta[++ top] = x;
int i, y;
for (i = head[x]; i; i = nex[i])
{
y = ver[i];
if (! dfn[y])
{
tarjan(y);
low[x] = min(low[x], low[y]);
}
else if (in[y]) low[x] = min(low[x], dfn[y]);
}
if (low[x] == dfn[x])
{
++ num;
do {
y = sta[top --], in[y] = 0;
tar[y] = num;
minv[num] = min(minv[num], v[y]);
maxv[num] = max(maxv[num], v[y]);
} while(x != y);
}
return;
}
int vers[M], nexs[M], heads[N], cnts, deg[N], deg1[N], maxv1[N];
inline void add(int x, int y)
{
vers[++ cnts] = y;
nexs[cnts] = heads[x];
++ deg[y];
return (void)(heads[x] = cnts);
}
inline void fuck1()
{
queue<int>q;
for (int i = 1; i <= num; ++ i)
{
if (! deg[i]) q.push(i);
maxv1[i] = maxv[i], deg1[i] = deg[i];
}
while (! q.empty())
{
int x = q.front(); q.pop();
for (int i = heads[x]; i; i = nexs[i])
{
int y = vers[i];
maxv[y] = max(maxv[y], maxv[x]);
if (! --deg1[y]) q.push(y);
}
res = max(res, maxv[x] - minv[x]);
}
return;
}
inline void fuck2()
{
queue<int>q;
for (int i = 1; i <= num; ++ i) if (! deg[i]) q.push(i);
while (! q.empty())
{
int x = q.front(); q.pop();
for (int i = heads[x]; i; i = nexs[i])
{
int y = vers[i];
minv[y] = min(minv[y], minv[x]);
if (! --deg[y]) q.push(y);
}
res = max(res, maxv1[x] - minv[x]);
}
}
signed main()
{
int i, x, y; n = read(), m = read();
memset(minv, 0x3f, sizeof minv), memset(maxv, 0xcf, sizeof maxv);
for (i = 1; i <= n; ++ i) v[i] = read();
for (i = 1; i <= m; ++ i)
{
x = read(), y = read();
if (existed[pr(x, y)]) continue;
add_edge(x, y);
existed[pr(x, y)] = 1;
}
for (i = 1; i <= n; ++ i) if (! dfn[i]) tarjan(i);
for (x = 1; x <= n; ++ x)
{
for (i = head[x]; i; i = nex[i])
{
y = ver[i];
if (tar[x] == tar[y]) continue;
add(tar[x], tar[y]);
}
}
fuck1(), fuck2();
put(res);
return 0;
}
|