AC 250, tried atcoder virtual contest, wasn't even half bad

atcoder/beginner_contests/250/c.cpp

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+#include <bits/stdc++.h>
+
+using namespace std;
+
+int main(){
+    ios::sync_with_stdio(0);
+    cin.tie(0);
+
+    int n, q;
+    cin >> n >> q;
+
+    // Denoting what ball is on the ith position
+    vector<int> numberBall(n);
+    // Denoting where the ith ball is
+    vector<int> ballPosition(n);
+
+    for(int i = 0; i < n; ++i){
+        numberBall[i] = i;
+        ballPosition[i] = i;
+    }
+
+    for(int j = 0; j < q; ++j){
+        int xq;
+        cin >> xq;
+        xq--;
+
+        int x_pos = ballPosition[xq], y_pos, yq;
+
+        if(x_pos != n - 1){
+            y_pos = x_pos + 1;
+            yq = numberBall[y_pos];
+
+            swap(numberBall[x_pos], numberBall[y_pos]);
+            swap(ballPosition[xq], ballPosition[yq]);
+        } else{
+            y_pos = x_pos - 1;
+            yq = numberBall[y_pos];
+
+            swap(numberBall[x_pos], numberBall[y_pos]);
+            swap(ballPosition[xq], ballPosition[yq]);
+        }
+    }
+
+    for(int i = 0; i < n; ++i){
+        cout << numberBall[i] + 1 << " ";
+    } cout << endl;
+
+    cout << flush;
+
+    return 0;
+}