實現一個二叉搜索樹迭代器。你將使用二叉搜索樹的根節點初始化迭代器。
調用 next()
將返回二叉搜索樹中的下一個最小的數。
/**
* Definition for a binary tree node.
* struct TreeNode {
* int val;
* TreeNode *left;
* TreeNode *right;
* TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class BSTIterator {
stack<TreeNode*>s;
TreeNode *cur;
public:
BSTIterator(TreeNode* root) {
this->cur=root;
}
/** @return the next smallest number */
int next() {
int res=INT_MAX;
while(cur||s.size()){
while(cur){
s.push(cur);
cur=cur->left;
}
cur=s.top();
res=cur->val;
s.pop();
cur=cur->right;
break;
}
return res;
}
/** @return whether we have a next smallest number */
bool hasNext() {
return cur||s.size();
}
};
/**
* Your BSTIterator object will be instantiated and called as such:
* BSTIterator* obj = new BSTIterator(root);
* int param_1 = obj->next();
* bool param_2 = obj->hasNext();
*/
輸入一個字符串,按字典序打印出該字符串中字符的所有排列。例如輸入字符串abc,則打印出由字符a,b,c所能排列出來的所有字符串abc,acb,bac,bca,cab和cba。
輸入描述:
輸入一個字符串,長度不超過9(可能有字符重複),字符只包括大小寫字母。
class Solution {
vector<string> res;
string sel,path;
bitset<9>b;
public:
vector<string> Permutation(string str) {
if(str.size()==0)return {};
sel=str;
sort(sel.begin(),sel.end());
backTrack();
return res;
}
void backTrack(){
if(path.size()==sel.size()){
res.push_back(path);
return ;
}
for(int i=0;i<sel.size();++i){
if(b[i])continue;
if(i>0&&!b[i-1]&&sel[i]==sel[i-1])continue;//去重最關鍵!!!
path.push_back(sel[i]);
b[i]=1;
backTrack();
b[i]=0;
path.pop_back();
}
}
};