permutations

Author: zhongn2

Diff for: Permutations II.cpp

@@ -0,0 +1,32 @@
+// Permutations II
+// method1: use hashmap to record and swap i with j( j = i .....n)
+
+class Solution {
+public:
+    vector<vector<int> > permuteUnique(vector<int> &num) {
+        vector<vector<int> > result;
+        if(num.size()== 0) return result;
+        vector<int> path;
+        dfs(result, path, num, 0);
+        return result;
+    }
+    void dfs(vector<vector<int> > &result, vector<int> &path, vector<int> &num, int index){
+        if(index == num.size()){
+            result.push_back(path);
+            return;
+        }
+        unordered_set<int> hashmap;
+        for(int i = index; i < num.size(); i++){
+            // the element is not in hashmap
+            if(hashmap.find(num[i]) == hashmap.end()){
+                hashmap.insert(num[i]);
+                swap(num[index], num[i]);
+                path.push_back(num[index]);
+                dfs(result, path, num, index + 1);
+                path.pop_back();
+                swap(num[index], num[i]);
+            }
+        }
+        
+    }
+};

Diff for: permutation.cpp

@@ -0,0 +1,26 @@
+class Solution {
+public:
+    vector<vector<int> > permute(vector<int> &num) {
+        sort(num.begin(), num.end()); // sort 
+        vector<vector<int> > result; // final answer
+        vector<int> path; // current path
+        dfs(result, path, num); // depth first search
+        return result;
+    }
+private:
+    void dfs(vector<vector<int> > &result, vector<int> &path, vector<int> &num){
+        if(path.size() == num.size()){ // find one path
+            result.push_back(path);
+            return;
+        }
+        for(auto i: num){
+            auto pos = find(path.begin(), path.end(), i); // return the pos or the last
+            if(pos == path.end()){
+                path.push_back(i);
+                dfs(result, path, num);
+                path.pop_back();
+            }
+        }
+        
+    }
+};