[LeetCode]-001-Two Sum
題意:
給一組數,給一個目標值.
這組數裡有2個數的和等於目標值,求出這兩個數的下標.
提示:
下標從1開始
明確一定有答案
分析:
一定有答案,從而不用對特殊情況進行考慮.
比如:
(1)一組數的長度小於2.
(2)沒有答案
(3)和值等於2個相同下標的數的和
解法:
想法1:
排序,2個index,1個從前,1個從後,通過和與目標值比較.
但最終求得是下標,所以額外空間存下標與排序同時顯得很麻煩.
想法2:
這組數相對雜湊,把value和key倒置.
因為對值的範圍不明,map就是一個很好的選擇.
C++中的unordered_map是無序map,同時也是最高效的map
利用它,很快得到一個不錯的結果
Java中沒有unordered_map,無序map用HashMap.
程式碼:
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