LeetCode216. 组合总和III
题目链接:216. 组合总和III
独上高楼,望尽天涯
继续复健,一直在犯小的语法错误。
慕然回首,灯火阑珊
和昨天的题很像,主要区别在于递归返回条件和回溯过程。
class Solution {
private:
vector<vector<int>> result;
vector<int> path;
void backtracking(int k, int target_sum, int start_index) {
if (path.size() == k) {
if (target_sum == 0) result.push_back(path);
return;
}
for (int i = start_index; i <= 9; i++) { // 注意中间是<=
target_sum -= i;
path.push_back(i);
backtracking(k, target_sum, i+1);
target_sum += i;
path.pop_back();
}
}
public:
vector<vector<int>> combinationSum3(int k, int n) {
backtracking(k, n, 1);
return result;
}
};
剪枝操作
class Solution {
private:
vector<vector<int>> result;
vector<int> path;
void backtracking(int k, int target_sum, int start_index) {
if (target_sum < 0) { // 剪枝操作
return;
}
if (path.size() == k) {
if (target_sum == 0) result.push_back(path);
return;
}
for (int i = start_index; i <= 9 - (k - path.size()) + 1; i++) { // 剪枝操作
target_sum -= i;
path.push_back(i);
backtracking(k, target_sum, i+1);
target_sum += i;
path.pop_back();
}
}
public:
vector<vector<int>> combinationSum3(int k, int n) {
backtracking(k, n, 1);
return result;
}
};
LeetCode17. 电话号码的字母组合
题目链接:17. 电话号码的字母组合
独上高楼,望尽天涯
思路不难,细节很多,写起来有点浆糊。
慕然回首,灯火阑珊
class Solution {
private:
const string letter_map[10] = {
"",
"",
"abc",
"def",
"ghi",
"jkl",
"mno",
"pqrs",
"tuv",
"wxyz"
};
vector<string> result;
string path;
void backtracking(const string& digits, int index) {
if (path.size() == digits.size()) {
result.push_back(path);
return;
}
int digit = digits[index] - '0'; // char转int小技巧
string letter = letter_map[digit];
for (int i = 0; i < letter.size(); i++) {
path.push_back(letter[i]); // 处理
backtracking(digits, index+1); //递归
path.pop_back(); // 回溯
}
}
public:
vector<string> letterCombinations(string digits) {
if (digits.size() == 0) {
return result;
}
backtracking(digits, 0);
return result;
}
};
标签:index,return,day25,int,result,LeetCode17,字母组合,path,backtracking
From: https://www.cnblogs.com/BarcelonaTong/p/17067756.html