Practice · 4 of 5
Debug: Backwards Sort
**Description:** The program must sort n pairs by their first element ASCENDING
(ties: any order) and print the first elements. Find and fix the bug.
**Broken code:**
``cpp
void solve(std::istream& in, std::ostream& out) {
int n; in >> n;
vector<pair<int,int>> v(n);
for (auto& p : v) in >> p.first >> p.second;
sort(v.begin(), v.end(), [](const pair<int,int>& x, const pair<int,int>& y) {
return x.first > y.first;
});
for (int i = 0; i < n; ++i)
out << v[i].first << (i + 1 < n ? " " : "");
out << "\\n";
}
`
**Input:** Line 1: n (1 <= n <= 100000). Next n lines: a b (|a|, |b| <= 10^9).
**Output:** One line: the first elements in ascending order, space-separated.
**Example:** 3 / 3 0 / 1 9 / 2 4 -> 1 2 3`.
Back to lesson: Practice: Debugging Problem Set