代码1

class Solution {
public:
    string mergeAlternately(string w1, string w2) {
        string s;
        int n = w1.size(), m = w2.size(), i = 0, j = 0;
        while(i<n && j<m){
            s+=w1[i++];
            s+=w2[j++];
        }
        while(i<n) s+=w1[i++];
        while(j<m) s+=w2[j++];

        return s;
    }
};

代码2

class Solution {
public:
    string mergeAlternately(string a, string b) {
        string res;
        int i = 0, j = 0;
        while (i < a.size() || j < b.size()) {
            if (i < a.size()) res += a[i ++ ];
            if (j < b.size()) res += b[j ++ ];
        }
        return res;
    }
};