LeetCode Java First 400 题解-028

mac2025-01-30  21

Implement strStr()   Easy

Implement strStr().

Returns the index of the first occurrence of needle in haystack, or -1 if needle is not part of haystack.

public int strStr(String haystack, String needle) {     if (haystack == null || needle == null)         return -1;     int m = haystack.length();     int n = needle.length();     Set<String> ns = new HashSet<String>() {{         add(needle);     }};     for (int i = 0; i < m - n + 1; ++i) {         String cur = haystack.substring(i, i + n);         if (ns.contains(cur))             return i;     }     return -1; }

思路:取得haystack中每一个与needle等长的子串,取Hash与needle相比,然后再计算是否相等。 O(n)

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