D - Circular Spanning Tree

https://codeforces.com/contest/1682/submission/158080863

Codeforces/1682/D/D.cpp

@@ -0,0 +1,54 @@
+#include <iostream>
+#include <string>
+
+using std::cin;
+using std::cout;
+const char endl = '\n';
+
+int t, n;
+std::string s;
+
+inline int pre(int x) {
+    return x == 1 ? n : x - 1;
+}
+
+inline int nxt(int x) {
+    return x == n ? 1 : x + 1;
+}
+
+int main() {
+    std::ios::sync_with_stdio(false);
+
+    cin >> t;
+
+    while (t--) {
+        int cnt = 0;
+
+        cin >> n >> s;
+
+        for (char c : s) {
+            if (c == '1') cnt++;
+        }
+
+        if (!cnt || (cnt & 1)) {
+            cout << "NO" << endl;
+        } else {
+            cout << "YES" << endl;
+
+            int lst = 0;
+            for (int i = 1; i <= n; i++) {
+                if (s[i - 1] == '1') lst = nxt(i);
+            }
+
+            for (int i = nxt(lst); i != lst; i = nxt(i)) {
+                if (i == nxt(lst) || s[pre(i) - 1] == '1') {
+                    cout << lst << ' ' << i << endl;
+                } else {
+                    cout << pre(i) << ' ' << i << endl;
+                }
+            }
+        }
+    }
+
+    return 0;
+}