216.组合总和III
思路:
以回溯函数做对称,上面做了什么操作,下面也是
java
class Solution {
List<List<Integer>> result = new ArrayList<>();
LinkedList<Integer> path = new LinkedList<>();
public List<List<Integer>> combinationSum3(int k, int n) {
travelsal(k, n, 1, 0);
return result;
}
private void travelsal(int k, int n, int startIndex, int sum) {
if (sum == n && path.size() == k) {
result.add(new ArrayList<>(path));
return;
}
for (int i = startIndex; i <= 9 - (k - path.size()) + 1; i++) {
if (sum > n || path.size() > k)
break;
path.add(i);
sum += i;
travelsal(k, n, i + 1, sum);
sum -= i;
path.removeLast();
}
}
}
17.电话号码的字母组合
思路:思路上和组合很像,不同的是对字符串进行操作
java
class Solution {
List<String> list = new ArrayList<>();
public List<String> letterCombinations(String digits) {
if (digits == null || digits.length() == 0)
return list;
String[] numString = { "", "", "abc", "def", "ghi", "jkl", "mno", "pqrs", "tuv", "wxyz" };
travelsal(digits, numString, 0);
return list;
}
StringBuilder temp = new StringBuilder();
public void travelsal(String digits, String[] numString, int num) {
if (num == digits.length()) {
list.add(temp.toString());
return;
}
String str = numString[digits.charAt(num) - '0'];
for (int i = 0; i < str.length(); i++) {
temp.append(str.charAt(i));
travelsal(digits, numString, num + 1);
temp.deleteCharAt(temp.length() - 1);
}
}
}
还得再想想