相邻两个是相等高度的才能达到任意高度，像 1221 这种也不行。如果最后剩下一个未匹配成功的，那么一定要是最高的。（因为只能横着放）
那么用栈维护一下就好了。
#include <bits/stdc++.h>
#define reg register
#define ll long long
#define ull unsigned long long
#define db double
#define pi pair<int, int>
#define pl pair<ll, ll>
#define vi vector<int>
#define vl vector<ll>
#define vpi vector<pi>
#define vpl vector<pl>
#define pb push_back
#define er erase
#define SZ(x) (int) x.size()
#define lb lower_bound
#define ub upper_bound
#define all(x) x.begin(), x.end()
#define rall(x) x.rbegin(), x.rend()
#define mkp make_pair
#define ms(data_name) memset(data_name, 0, sizeof(data_name))
#define msn(data_name, num) memset(data_name, num, sizeof(data_name))
#define For(i, j) for(reg int (i) = 1; (i) <= (j); ++(i))
#define For0(i, j) for(reg int (i) = 0; (i) < (j); ++(i))
#define Forx(i, j, k) for(reg int (i) = (j); (i) <= (k); ++(i))
#define Forstep(i , j, k, st) for(reg int (i) = (j); (i) <= (k); (i) += (st))
#define fOR(i, j) for(reg int (i) = (j); (i) >= 1; (i)--)
#define fOR0(i, j) for(reg int (i) = (j) - 1; (i) >= 0; (i)--)
#define fORx(i, j, k) for(reg int (i) = (k); (i) >= (j); (i)--)
#define tour(i, u) for(reg int (i) = head[(u)]; (i) != -1; (i) = nxt[(i)])
using namespace std;
char ch, B[1 << 20], *S = B, *T = B;
#define getc() (S == T && (T = (S = B) + fread(B, 1, 1 << 20, stdin), S == T) ? 0 : *S++)
#define isd(c) (c >= '0' && c <= '9')
int rdint() {
int aa, bb;
while(ch = getc(), !isd(ch) && ch != '-');
ch == '-' ? aa = bb = 0 : (aa = ch - '0', bb = 1);
while(ch = getc(), isd(ch))
aa = aa * 10 + ch - '0';
return bb ? aa : -aa;
}
ll rdll() {
ll aa, bb;
while(ch = getc(), !isd(ch) && ch != '-');
ch == '-' ? aa = bb = 0 : (aa = ch - '0', bb = 1);
while(ch = getc(), isd(ch))
aa = aa * 10 + ch - '0';
return bb ? aa : -aa;
}
const int mod = 998244353;
// const int mod = 1e9 + 7;
struct mod_t {
static int norm(int x) {
return x + (x >> 31 & mod);
}
int x;
mod_t() { }
mod_t(int v) : x(v) { }
mod_t(ll v) : x(v) { }
mod_t(char v) : x(v) { }
mod_t operator +(const mod_t &rhs) const {
return norm(x + rhs.x - mod);
}
mod_t operator -(const mod_t &rhs) const {
return norm(x - rhs.x);
}
mod_t operator *(const mod_t &rhs) const {
return (ll) x * rhs.x % mod;
}
};
const int MAXN = 2e5 + 10;
int n, a[MAXN], stk[MAXN], top = 0;
inline void work() {
n = rdint();
int mx = 0;
For(i, n) {
a[i] = rdint();
mx = max(mx, a[i]);
}
bool flag = 0;
For(i, n) {
if(top != 0 && stk[top] == a[i])
top--;
else if(top != 0 && stk[top] < a[i])
flag = 1;
else
stk[++top] = a[i];
}
if(!flag && (top == 0 || top == 1 && stk[top] == mx))
printf("YES
");
else
printf("NO
");
}
int main() {
// freopen("input.txt", "r", stdin);
work();
return 0;
}