判断s是否是t的子序列

class Solution {
public:
    bool isSubsequence(string s, string t) {
        int n=s.length(),m=t.length();
        int i=0,j=0;
        while(i<n && j<m){
            if(s[i]==t[j]){
                i++;
            }
            j++;
        }
        return i==n;
    }
};