1+ /*
2+ * Deleted code is debugged code :)
3+ */
4+ #include < bits/stdc++.h>
5+ #define ll long long
6+ #define ull unsigned long long
7+ #define vi vector<ll>
8+ #define pp pair<ll,ll>
9+ #define mp make_pair
10+ #define PI acos (-1.0 )
11+ #define all (v ) v.begin(),v.end()
12+ #define pb push_back
13+ #define FOR (i,a,b ) for (i=a;i<b;i++)
14+ #define FREV (i,a,b ) for (i=a;i>=b;i--)
15+ #define SULL (n ) scanf(" %llu"
16+ #define INF 1e18
17+ #define MOD 1000000007
18+ 19+ #ifndef ONLINE_JUDGE
20+ #define gc getchar
21+ #define pc putchar
22+ #else
23+ #define gc getchar_unlocked
24+ #define pc putchar_unlocked
25+ #endif
26+ 27+ using namespace std ;
28+ 29+ int read_int () {
30+ char c = gc ();
31+ while ((c < ' 0' ' 9' ' -' gc ();
32+ int ret = 0 , neg = 0 ;
33+ if (c == ' -' 1 , c = gc ();
34+ while (c >= ' 0' ' 9'
35+ ret = 10 * ret + c - 48 ;
36+ c = gc ();
37+ }
38+ return neg ? -ret : ret;
39+ }
40+ 41+ ll read_ll () {
42+ char c = gc ();
43+ while ((c < ' 0' ' 9' ' -' gc ();
44+ ll ret = 0 ;
45+ int neg = 0 ;
46+ if (c == ' -' 1 , c = gc ();
47+ while (c >= ' 0' ' 9'
48+ ret = 10 * ret + c - 48 ;
49+ c = gc ();
50+ }
51+ return neg ? -ret : ret;
52+ }
53+ 54+ /* ******************************************RANDOM STUFF BEGINS HERE**************************************************/
55+ 56+ struct node {
57+ vi adj;
58+ };
59+ 60+ vector<node> tree;
61+ vi depth (100005 ), parent(100005 );
62+ 63+ // DFS to calculate depths of the nodes
64+ void dfs (ll u) {
65+ ll i, len = tree[u].adj .size ();
66+ FOR (i,0 ,len) {
67+ ll v = tree[u].adj [i];
68+ depth[v] = depth[u] + 1 ;
69+ dfs (v);
70+ }
71+ }
72+ 73+ // Preprocessing for LCA in O(nlogn)
74+ // binary_ancestor[i][j] stores the 2^j ancestor of node i
75+ 76+ ll binary_ancestor[1000005 ][20 ];
77+ 78+ void LCA_preprocessing (ll n) {
79+ ll i, j;
80+ 81+ for (i = 1 ; i <= n; i++) {
82+ for (j = 0 ; 1 << j <= n; j++) {
83+ binary_ancestor[i][j] = -1 ;
84+ }
85+ }
86+ 87+ for (i = 1 ; i <= n; i++) {
88+ binary_ancestor[i][0 ] = parent[i];
89+ }
90+ 91+ for (j = 1 ; 1 << j <=n; j++) {
92+ for (i = 1 ; i <= n; i++) {
93+ binary_ancestor[i][j] = binary_ancestor[binary_ancestor[i][j-1 ]][j-1 ];
94+ }
95+ }
96+ }
97+ 98+ ll getLCA (ll x, ll y) {
99+ ll i, temp, log;
100+ 101+ // make x the node with greater depth
102+ if (depth[x] < depth[y]) {
103+ temp = x, x = y, y = temp;
104+ }
105+ 106+ for (log = 1 ; 1 << log <= depth[x]; log++);
107+ log--;
108+ 109+ // bring x and y to the same level
110+ for (i = log; i >= 0 ; i--) {
111+ if (depth[x] - (1 << i) >= depth[y]) {
112+ x = binary_ancestor[x][i];
113+ }
114+ }
115+ 116+ // x and y are now at the same level
117+ for (i = log; i >= 0 ; i--) {
118+ if (binary_ancestor[x][i] != -1 && binary_ancestor[x][i] != binary_ancestor[y][i]) {
119+ x = binary_ancestor[x][i];
120+ y = binary_ancestor[y][i];
121+ }
122+ }
123+ 124+ return parent[x];
125+ }
126+ 127+ int main () {
128+ ll i,j,t,n,x,y;
129+ n = read_ll ();
130+ tree.resize (n+1 );
131+ // 1 is the root. Accept parents of the remaining (n-1) nodes
132+ FOR (i,2 ,n+1 ) {
133+ j = read_ll ();
134+ tree[j].adj .pb (i);
135+ parent[i] = j;
136+ }
137+ dfs (1 );
138+ LCA_preprocessing (n);
139+ x = read_ll ();
140+ y = read_ll ();
141+ cout << " LCA of " " and " " = " getLCA (x,y) << endl;
142+ return 0 ;
143+ }
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