Change condition in walk function for sum check

Author: lrvideckis

tests/library_checker_aizu_tests/data_structures/simple_tree_inc_walk.test.cpp

@@ -23,7 +23,7 @@ int main() {
     } else if (type == 3) {
       // returns first element in [k,n-1] such that sum > 0
       int idx = st.walk(k, n - 1, [&](int sum) {
-        return sum > 0;
+        return sum == 0;
       });
       if(idx == n) idx = -1;
       cout<<idx<<'\n';
@@ -35,8 +35,10 @@ int main() {
       } else {
         int pref_sum = 0;
         cout << st.walk(0, k, [&](int sum) {
-          if (pref_sum + sum == total) return 1;
-          pref_sum += sum;
+          if (pref_sum + sum < total) {
+            pref_sum += sum;
+            return 1;
+          }
           return 0;
         }) << '\n';
       }