diff --git a/baekjoon/7578_indexTree.cpp b/baekjoon/7578_indexTree.cpp
new file mode 100644
index 0000000..c293ab8
--- /dev/null
+++ b/baekjoon/7578_indexTree.cpp
@@ -0,0 +1,106 @@
+#include <iostream>
+#include <vector>
+#include <map>
+#include <queue>
+
+using namespace std;
+
+class IndexTree
+{
+public:
+    int leafLeft;
+    int treeSize;
+    vector<long long> v_tree;
+    IndexTree(int N)
+    {
+        for (leafLeft = 1; leafLeft < N; leafLeft *= 2)
+            ;
+        treeSize = leafLeft * 2;
+        v_tree.resize(treeSize);
+    }
+
+    long long logicFun(long long num1, long long num2)
+    {
+        return num1 + num2;
+    }
+
+    void updateTree(int index)
+    {
+        if (index == 0)
+            return;
+        v_tree[index] = logicFun(v_tree[2 * index], v_tree[2 * index + 1]);
+        updateTree(index / 2);
+    }
+
+    void add(int order)
+    {
+        int index = leafLeft + order - 1;
+        v_tree[index]++;
+        updateTree(index / 2);
+    }
+
+    long long query(int begin, int end)
+    {
+        int L = leafLeft + begin - 1;
+        int R = leafLeft + end - 1;
+
+        long long result = 0;
+        while (L < R)
+        {
+            int nextL = (L + 1) / 2;
+            int nextR = (R - 1) / 2;
+
+            if (nextL != L / 2)
+                result = logicFun(result, v_tree[L]);
+            if (nextR != R / 2)
+                result = logicFun(result, v_tree[R]);
+
+            L = nextL;
+            R = nextR;
+        }
+        if (L == R)
+            result = logicFun(result, v_tree[L]);
+        return result;
+    }
+};
+
+int N;
+map<int, int> m_idIndex;
+
+void solution()
+{
+    priority_queue<pair<int, int>> pq;
+    int ident;
+    cin >> N;
+    for (int i = 1; i <= N; i++)
+    {
+        cin >> ident;
+        m_idIndex[ident] = i;
+    }
+    for (int i = 1; i <= N; i++)
+    {
+        cin >> ident;
+        int index = m_idIndex[ident];
+        pq.push(make_pair(index, i));
+    }
+
+    IndexTree indexTreeCount(N);
+    long long totalCount = 0;
+    while (!pq.empty())
+    {
+        auto machine = pq.top();
+        pq.pop();
+        long long count = indexTreeCount.query(1, machine.second);
+        totalCount += count;
+        indexTreeCount.add(machine.second);
+    }
+    cout << totalCount << "\n";
+}
+
+int main()
+{
+    ios_base::sync_with_stdio(false);
+    cin.tie(NULL);
+    solution();
+    return 0;
+}
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