相似的事物放一起，是讓環境井然有序的關鍵，這也是電腦世界中陣列（Array）此資料結構的設計理念。 因為事物都在同處，我們可藉索引在常數時間（O(1)）內找到對應元素（隨機存取）。
如果不是相似的事物，如果不放在一起，我們還有方法能好好整理它們嗎？可以，用鍵（Key）值（Value）架構即可。 我們先定好一個雜湊（Hashing）函數，讓要管理的事物都依循此函數的判斷放到對應區塊中。這樣就能在常數時間（O(1)）內找到鍵所對應的值。
Notes:
- 有時反向遍歷陣列，做法會簡單很多
- 程式碼要一開始就簡潔很難，寫完再整理比較容易
- 善用陣列索引的有序性，有時會比雜湊表還好用
跨倉庫導讀#
#1
Two Sum
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Longest Common Prefix
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Remove Element
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Find The Index of The First Occurrence in a String
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First Missing Positive
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