Create backtrack.java

backtrack.java

@@ -0,0 +1,54 @@
+//problem1
+class Solution {
+    List<List<Integer>> res;
+    public List<List<Integer>> subsets(int[] nums) {
+        this.res=new ArrayList<>();
+        helper(nums,0,new ArrayList<>());
+        return res;
+    }
+    public void helper(int[] nums,int pivot,List<Integer> path){
+        res.add(new ArrayList<>(path));
+        for(int i=pivot;i<nums.length;i++){
+            path.add(nums[i]);
+            helper(nums,i+1,path);
+            path.remove(path.size()-1);
+        }
+    }
+}
+//problem2
+class Solution {
+    List<List<String>> ans;
+    public List<List<String>> partition(String s) {
+         this.ans=new ArrayList<>();
+        helper(s,0,new ArrayList<>());
+        return ans;
+    }
+    public void helper(String s,int pivot,List<String> path){
+        //base
+        if(pivot==s.length()){
+            ans.add(new ArrayList<>(path));
+            return;
+        }
+
+
+        //logic
+        for(int i=pivot;i<s.length();i++){
+            String curr=s.substring(pivot,i+1);
+            if(isplaindrome(curr)){
+                path.add(curr);
+                helper(s,i+1,path);
+                path.remove(path.size()-1);
+            }
+        }
+    }
+    public boolean isplaindrome(String s){
+        int l=0;
+        int r=s.length()-1;
+        while(l<r){
+            if(s.charAt(l)!=s.charAt(r)) return false;
+            l++;
+            r--;
+        }
+        return true;
+    }
+}