排序後處理 Sort then Scan
48 題（0 題以此為主技法）
🎯 何時用
先排序能讓貪心、雙指針、掃描變得簡單（區間、配對、相鄰關係）。
🧩 模板心法
依關鍵字排序後一次掃描；常與貪心或雙指針搭配。注意排序鍵與穩定性。
Easy 7 題
Medium 35 題
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