Sub sequence occurrence in a string

Question

Given 2 strings like bangalore and blr, return whether one appears as a subsequence of the other. The above case returns true whereas bangalore and brl returns false.

Answer 1

O(N) solution, where N is the length of the substring.

bool subsequence( string s1, string s2 ){
    int n1 = s1.length();
    int n2 = s2.length();

    if( n1 > n2 ){
        return false;
    }

    int i = 0;
    int j = 0;
    while( i < n1 && j < n2 ){
        if( s1[i] == s2[j] ){
            i++;
        } 
        j++;
    }

    return i == n1;
}