keep going

amazon.cpp

@@ -1413,6 +1413,173 @@ public:
         return res;
     }
 };
+
+
+
+
+Permutations
+//solution1, 用swap，每个都会到第一个的原理, backtracking
+class Solution {
+public:
+    vector<vector<int>> permute(vector<int>& nums) {
+        vector<vector<int>> res;
+        helper(nums,  , res);
+        return res;
+    }
+    
+    void helper(vector<int> &nums, int &level ,vector<vector<int>>& res){
+        if(level == nums.size()) {res.push_back(nums); return;}
+        else{
+            for(int i=level; i<nums.size(); i++){
+                swap(nums[i], nums[level]);
+                helper(nums, level+1, res);
+                swap(nums[level], nums[i]);
+            }
+        }
+    }
+};
+
+
+//solution2, backtracking, 用了排列组合，往pool里取char的方式
+class Solution {
+public:
+    vector<vector<int>> permute(vector<int>& nums) {
+        vector<vector<int>> res;
+        vector<int> current;
+        helper(res, nums, current);
+        return res;
+    }
+    
+    void helper(vector<vector<int>>& res, vector<int>& pool, vector<int>& current){
+        if (!pool.size()) {res.push_back(current);}
+        else{
+            for(int i=0; i<pool.size(); i++){
+                current.push_back(pool[i]);
+                vector<int> temp (pool.begin(), pool.end());
+                temp.erase(temp.begin()+i);
+                helper(res, temp, current);
+                current.pop_back();
+            }
+        }
+    }
+};
+
+
+78. Subsets
+// backtracking问题训练集！ 同上一题
+class Solution {
+public:
+    vector<vector<int>> subsets(vector<int>& nums) {
+        vector<vector<int>> res;
+        for(int i=0; i<nums.size()+1; i++){
+            vector<vector<int>> temp;
+            vector<int> current;
+            helper(i, nums, current, temp);
+            res.insert(res.end(), temp.begin(), temp.end());
+        }
+        return res;
+    }
+    
+    void helper(int goal, vector<int>& pool, vector<int>& current, vector<vector<int>>& res){
+        if(current.size() == goal) {res.push_back(current); }
+        else{
+            for(int i=0; i<pool.size(); i++){
+                current.push_back(pool[i]);
+                vector<int> temp(pool.begin()+i+1, pool.end());
+                helper(goal, temp, current, res);
+                current.pop_back();
+            }
+        }
+    }
+    
+};
+
+
+Meeting Rooms II
+//priority_quueue 真的很实用很重要！尤其是在只考虑当前最小或者最大的时候！
+class Solution {
+public:
+    struct compartor{
+        bool operator() (const vector<int> &a, const vector<int> &b){
+            return a[1] > b[1];
+        }
+};
+    
+    int minMeetingRooms(vector<vector<int>>& intervals) {
+        sort(intervals.begin(), intervals.end());
+        priority_queue<vector<int>, vector<vector<int>>, compartor> pq;
+        if(intervals.empty()) return 0;
+        
+        pq.push(intervals[0]);
+        int rooms = 1;
+        for(int i=1; i<intervals.size(); i++){
+            if(pq.top()[1] >intervals[i][0]) rooms++;
+            else{
+                pq.pop();
+            }
+            pq.push(intervals[i]);
+        }
+        return rooms;
+    }
+};
+
+
+
+
+
+
+//Subsets II (contains duplicates) : https://leetcode.com/problems/subsets-ii/
+// backtracking问题训练集！
+
+
+
+//Permutations : https://leetcode.com/problems/permutations/
+// backtracking问题训练集！
+
+
+//Permutations II (contains duplicates) : https://leetcode.com/problems/permutations-ii/
+// backtracking问题训练集！
+
+
+
+//Combination Sum : https://leetcode.com/problems/combination-sum/
+// backtracking问题训练集！
+
+
+
+//Combination Sum II (can't reuse same element) : https://leetcode.com/problems/combination-sum-ii/
+// backtracking问题训练集！
+
+
+
+//Palindrome Partitioning : https://leetcode.com/problems/palindrome-partitioning/
+// backtracking问题训练集！
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+