#pragma GCC optimize(2)
#pragma GCC optimize(3)
#pragma GCC optimize(4)
#include<bits/stdc++.h>
using namespace std;
#define fi first
#define se second
#define pi acos(-1.0)
#define LL long long
//#define mp make_pair
#define pb push_back
#define ls rt<<1, l, m
#define rs rt<<1|1, m+1, r
#define ULL unsigned LL
#define pll pair<LL, LL>
#define pli pair<LL, int>
#define pii pair<int, int>
#define piii pair<pii, int>
#define mem(a, b) memset(a, b, sizeof(a))
#define fio ios::sync_with_stdio(false);cin.tie(0);cout.tie(0);
#define fopen freopen("in.txt", "r", stdin);freopen("out.txt", "w", stout);
//head#define ck(l, x, y, z) a[l]==x&&a[l+1]==y&&a[l+2]==z
#define ckk(r, x, y, z) a[r]==x&&a[r-1]==y&&a[r-2]==z
const int N = 1e5 + 10;
int a[N], tmp[N], n;
vector<piii> ans;
bool f = false;
void flip(int x, int y, int z) {a[x] ^= 1;a[y] ^= 1;a[z] ^= 1;ans.pb({{x, y}, z});
}
void fflip(int x, int y) {a[x] ^= 1;a[x+y>>1] ^= 1;a[y] ^= 1;ans.pb({{x, x+y>>1}, y});
}
void Flip(int x, int y) {tmp[x] ^= 1;tmp[x+y>>1] ^= 1;tmp[y] ^= 1;//ans.pb({{x, x+y>>1}, y});
}
void bruteforce(int l, int r) {vector<pii> vc;for (int i = l; i <= r; i++) {for (int j = i+2; j <= r; j += 2) {vc.pb({i, j});}}int sz = vc.size();for (int i = 0; i < (1<<sz); i++) {for (int j = l; j <= r; j++) tmp[j] = a[j];for (int j = 0; j < sz; j++) {if(i&(1<<j)) {Flip(vc[j].fi, vc[j].se);}}bool ff = true;for (int j = l; j <= r; j++) if(tmp[j]) {ff = false; break;}if(ff) {f = true;for (int j = 0; j < sz; j++) if(i&(1<<j))ans.pb({{vc[j].fi, vc[j].fi + vc[j].se >> 1}, vc[j].se});return ;}}
}
void solve(int l, int r) {if(r - l + 1 <= 8) {while(r-l+1 < 8 && l > 1) l--;while(r-l+1 < 8 && r < n) r++;bruteforce(l, r);return ;}if(a[l] == 0) {solve(l+1, r);return ;}if(a[r] == 0) {solve(l, r-1);return ;}if(ck(l, 1, 1, 1)) {flip(l, l+1, l+2);solve(l+3, r);return ;}if(ck(l, 1, 0, 1)) {flip(l, l+2, l+4);solve(l+3, r);return ;}if(ck(l, 1, 0, 0)) {flip(l, l+3, l+6);solve(l+3, r);return ;}if(ckk(r, 1, 1, 1)) {flip(r, r-1, r-2);solve(l, r-3);return ;}if(ckk(r, 1, 0, 1)) {flip(r, r-2, r-4);solve(l, r-3);return ;}if(ckk(r, 1, 0, 0)) {flip(r, r-3, r-6);solve(l, r-3);return ;}if((r-l+1)&1) {fflip(l, r);fflip(l+1, r-1);solve(l+3, r-3);return ;}else {fflip(l, r-1);fflip(l+1, r);solve(l+3, r-3);return ;}
}
int main() {int cnt = 0;scanf("%d", &n);for (int i = 1; i <= n; i++) scanf("%d", &a[i]);solve(1, n);if(f) {printf("YES\n");printf("%d\n", (int)ans.size());for (piii p : ans) printf("%d %d %d\n", p.fi.fi, p.fi.se, p.se);}else printf("NO\n");return 0;
}