Permutation In String Problem


Description

LeetCode Problem 567.

Given two strings s1 and s2, return true if s2 contains a permutation of s1, or false otherwise. In other words, return true if one of s1’s permutations is the substring of s2.

Example 1:

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Input: s1 = "ab", s2 = "eidbaooo"
Output: true
Explanation: s2 contains one permutation of s1 ("ba").

Example 2:

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Input: s1 = "ab", s2 = "eidboaoo"
Output: false

Constraints:

  • 1 <= s1.length, s2.length <= 10^4
  • s1 and s2 consist of lowercase English letters.


Sample C++ Code

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class Solution {
public:    
    bool checkInclusion(string s1, string s2) {
        int l1 = s1.size(), l2 = s2.size();
        if (l1 > l2) return false;
        
        vector<int> m(26, 0);
        
        for (int i = 0; i < l1; i ++) {
            m[s1[i] - 'a'] ++;
            m[s2[i] - 'a'] --;
        }
        
        bool contained = true;
        for (int i = 0; i < 26; i ++) {
            if (m[i] != 0) {
                contained = false;
                break;
            }
        }
        if (contained) return true;
        
        for (int i = l1; i < l2; i ++) {
            m[s2[i] - 'a'] --;
            m[s2[i-l1] - 'a'] ++;
            
            contained = true;
            for (int j = 0; j < 26; j ++) {
                if (m[j] != 0) {
                    contained = false;
                    break;
                }
            }
            if (contained) return true;
            
            
        }
        
        return false;
    }
};




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