Given a string S, we can transform every letter individually to be lowercase or uppercase to create another string. Return a list of all possible strings we could create.
Examples:
Input: S = "a1b2"
Output: ["a1b2", "a1B2", "A1b2", "A1B2"]
Input: S = "3z4"
Output: ["3z4", "3Z4"]
Input: S = "12345"
Output: ["12345"]
Note:
S
will be a string with length at most12
.S
will consist only of letters or digits.
本质上是排列问题,经典的dfs求解。将字符串看作一棵树,dfs遍历过程中修改node为大写或者小写字母即可!
解法1:
class Solution {
public:
vector<string> letterCasePermutation(string S) {
// A! use DFS
vector<string> ans;
dfs(ans, S, 0);
return ans;
}
void dfs(vector<string> &ans, string &S, int i) {
if(i==S.size()) {
ans.push_back(string(S));
return;
}
dfs(ans, S, i+1); #本质上就是等价于tree node的dfs(root.left)
if(S[i]>='a' && S[i]<='z') { #本质上就是等价于tree node的dfs(root.right) 如果有right的话
S[i]-=32;
dfs(ans, S, i+1);
} else if (S[i]>='A' && S[i]<='Z') {
S[i]+=32;
dfs(ans, S, i+1);
}
}
};
比我精简的写法:
class Solution {
void backtrack(string &s, int i, vector<string> &res) {
if (i == s.size()) {
res.push_back(s);
return;
}
backtrack(s, i + 1, res);
if (isalpha(s[i])) {
// toggle case
s[i] ^= (1 << 5);
backtrack(s, i + 1, res);
}
}
public:
vector<string> letterCasePermutation(string S) {
vector<string> res;
backtrack(S, 0, res);
return res;
}
};
使用BFS:本质上和tree的BFS一样,只是tree的node是字符串的char。
class Solution(object):
def letterCasePermutation(self, S):
"""
:type S: str
:rtype: List[str]
"""
# A! problem, use BFS
q = [S] # tree的层序遍历也一样
for i in range(0, len(S)):
if S[i].isalpha():
q += [s[:i] + chr(ord(s[i]) ^ 32) + s[i+1:] for s in q]
return q
另外一种写法:
def letterCasePermutation(self, S):
res = ['']
for ch in S:
if ch.isalpha():
res = [i+j for i in res for j in [ch.upper(), ch.lower()]]
else:
res = [i+ch for i in res]
return res
来源:oschina
链接:https://my.oschina.net/u/4366204/blog/4047108