From d611db93bd48d3c9446993faa890bde30a567b8d Mon Sep 17 00:00:00 2001
From: goo-gy <lkukh17@naver.com>
Date: Sat, 22 Jan 2022 22:50:34 +0900
Subject: [PATCH] 11438 LCA

---
 baekjoon/11438_LCA.cpp | 109 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 109 insertions(+)
 create mode 100644 baekjoon/11438_LCA.cpp

diff --git a/baekjoon/11438_LCA.cpp b/baekjoon/11438_LCA.cpp
new file mode 100644
index 0000000..f4e80a4
--- /dev/null
+++ b/baekjoon/11438_LCA.cpp
@@ -0,0 +1,109 @@
+#include <iostream>
+#include <vector>
+
+using namespace std;
+
+int N, M;
+int sizeExp;
+vector<vector<int>> vv_graph;
+vector<vector<int>> vv_tree;
+vector<bool> v_visit;
+vector<int> v_depth;
+
+void reset()
+{
+    for (sizeExp = 1; (1 << sizeExp) <= N; sizeExp++)
+        ;
+    v_visit.resize(N + 1, false);
+    v_depth.resize(N + 1);
+    vv_graph.resize(N + 1);
+    vv_tree.resize(N + 1);
+    for (int i = 0; i <= N; i++)
+        vv_tree[i].resize(sizeExp, 0);
+}
+
+void setAncestor(int node)
+{
+    for (int k = 1; k < sizeExp; k++)
+    {
+        int kAncestor = vv_tree[node][k - 1];
+        vv_tree[node][k] = vv_tree[kAncestor][k - 1];
+    }
+}
+
+void makeTreeDFS(int current, int depth)
+{
+    v_visit[current] = true;
+    v_depth[current] = depth;
+    for (auto next : vv_graph[current])
+    {
+        if (!v_visit[next])
+        {
+            vv_tree[next][0] = current;
+            setAncestor(next);
+            v_visit[next] = true;
+            makeTreeDFS(next, depth + 1);
+        }
+    }
+}
+
+int findLCA(int node1, int node2)
+{
+    int low = v_depth[node1] > v_depth[node2] ? node1 : node2;
+    int high = v_depth[node1] > v_depth[node2] ? node2 : node1;
+    int depthDiff = v_depth[low] - v_depth[high];
+    while (depthDiff > 0)
+    {
+        int expIndex;
+        for (expIndex = 0; (1 << expIndex) <= depthDiff; expIndex++)
+            ;
+        expIndex--;
+        low = vv_tree[low][expIndex];
+        depthDiff = v_depth[low] - v_depth[high];
+    }
+
+    int k = sizeExp - 1;
+    while (k >= 0)
+    {
+        int lowAn = vv_tree[low][k];
+        int highAn = vv_tree[high][k];
+        if (lowAn != highAn)
+        {
+            low = lowAn;
+            high = highAn;
+        }
+        k--;
+    }
+    if (low == high)
+        return low;
+    else
+        return vv_tree[low][0];
+}
+void solution()
+{
+    cin >> N;
+    reset();
+    for (int i = 1; i <= N - 1; i++)
+    {
+        int node1, node2;
+        cin >> node1 >> node2;
+        vv_graph[node1].push_back(node2);
+        vv_graph[node2].push_back(node1);
+    }
+    makeTreeDFS(1, 0);
+    cin >> M;
+    for (int i = 1; i <= M; i++)
+    {
+        int node1, node2;
+        cin >> node1 >> node2;
+        cout << findLCA(node1, node2) << "\n";
+    }
+}
+
+int main()
+{
+    ios_base::sync_with_stdio(false);
+    cin.tie(NULL);
+    solution();
+    return 0;
+}
\ No newline at end of file