LeetCode: 392-Is Subsequence 解題紀錄

Last Updated on 2022-03-02 by Clay

題目

Given two strings s and t, return true if s is a subsequence of t, or false otherwise.

A subsequence of a string is a new string that is formed from the original string by deleting some (can be none) of the characters without disturbing the relative positions of the remaining characters. (i.e., "ace" is a subsequence of "abcde" while "aec" is not).

Example 1:

Input: s = "abc", t = "ahbgdc"
Output: true

Example 2:

Input: s = "axc", t = "ahbgdc"
Output: false

Constraints:

• 0 <= s.length <= 100
• 0 <= t.length <= 104
• s and t consist only of lowercase English letters.

Follow up: Suppose there are lots of incoming s, say s1, s2, ..., sk where k >= 109, and you want to check one by one to see if t has its subsequence. In this scenario, how would you change your code?

題目輸入兩個字串 s 和 t，我們要判斷 t 刪減字元後是否可以還原成 s。

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解題思路

由於最近在忙面試，比較沒時間慢慢解…… 今天也就直接放了個非最佳解的 two-points 解法。

我知道存在著 DP 解，已經看過討論區了 XD

C++ 範例程式碼

class Solution {
public:
    bool isSubsequence(string s, string t) {
        // Base case
        if (s.empty()) return true;
        
        // Init
        int si = 0;
        
        // Match
        for (int ti=0; ti<t.size(); ++ti) {
            if (s[si] == t[ti]) {
                ++si;
            }
            
            if (si == s.size()) return true;
        }
        
        return false;
    }
};

Python 範例程式碼

class Solution:
    def isSubsequence(self, s: str, t: str) -> bool:
        # Base case
        if not s: return True
        
        # Init
        si = 0
        
        # Match
        for ti in range(len(t)):
            if s[si] == t[ti]:
                si += 1
            
            if si == len(s): return True
        
        return False

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References

• https://leetcode.com/problems/is-subsequence/

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