题目描述
Given an array of strings arr. String s is a concatenation of a sub-sequence of arr which have unique characters.
Return the maximum possible length of s.
Example 1:
Input: arr = ["un","iq","ue"]
Output: 4
Explanation: All possible concatenations are "","un","iq","ue","uniq" and "ique".
Maximum length is 4.
Example 2:
Input: arr = ["cha","r","act","ers"]
Output: 6
Explanation: Possible solutions are "chaers" and "acters".
Example 3:
Input: arr = ["abcdefghijklmnopqrstuvwxyz"]
Output: 26
Constraints:
1 <= arr.length <= 16
1 <= arr[i].length <= 26
arr[i] contains only lower case English letters.
思路
DFS,int数字表示当前字符串中是否有26个字母的状态。
代码
class Solution {
public:
int maxLength(vector<string>& arr) {
dfs(arr, 0, 0, "");
return ans;
}
private:
int ans = 0;
void dfs(vector<string>& arr, int cnt, int status, string cur) {
if (cnt == arr.size()) {
int len = cur.length();
ans = max(ans, len);
return;
}
string str = arr[cnt];
bool flag = true;
int ns = status;
for (const auto& ch: str) {
if ((status & (1<<(ch-'a'))) != 0) {
flag = false;
break;
}
status |= (1<<(ch-'a'));
}
if (flag) dfs(arr, cnt+1, status, cur+str);
dfs(arr, cnt+1, ns, cur);
return;
}
};