Add sort_maximal()

utilities/sort_maximal.hpp

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+#pragma once
+#include <algorithm>
+#include <utility>
+#include <vector>
+
+// Sort segments and erase not maximal ones
+// {{0, 2}, {1, 5}, {3, 4}} => {{0, 2}, {1, 5}}
+// {{1, 3}, {0, 1}, {1, 3}} => {{0, 1}, {1, 3}}  // remove duplicates
+// Verified: abc254g https://atcoder.jp/contests/abc254/tasks/abc254_g
+template <class T> std::vector<std::pair<T, T>> sort_maximal(std::vector<std::pair<T, T>> ranges) {
+    std::sort(ranges.begin(), ranges.end());
+    std::vector<std::pair<T, T>> ret;
+    for (const auto &p : ranges) {
+        if (!ret.empty() and ret.back().first == p.first) ret.pop_back();
+        if (ret.empty() or ret.back().second < p.second) ret.push_back(p);
+    }
+    return ret;
+}

utilities/sort_maximal.md

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+---
+title: 区間たちをソートし極大でないものを消去
+documentation_of: ./sort_maximal.hpp
+---
+
+## 使用方法
+
+```cpp
+vector<pair<int, int>> segs;
+segs = sort_maximal(segs);
+```
+
+## 問題例
+
+- [AtCoder Beginner Contest 254 G - Elevators](https://atcoder.jp/contests/abc254/tasks/abc254_g)