Spring permutations

Author: giaunv

datastructure-algorithm-java-examples/src/main/java/com/hellokoding/algorithm/BackTracking_StringPermutations.java

@@ -0,0 +1,41 @@
+package com.hellokoding.algorithm;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.stream.Collectors;
+
+public class BackTracking_StringPermutations {
+    List<String> result = new ArrayList<>();
+
+    String swap(String str, int i, int j) {
+        char[] arr = str.toCharArray();
+
+        char temp = arr[i];
+        arr[i] = arr[j];
+        arr[j] = temp;
+
+        return String.valueOf(arr);
+    }
+
+    void enumerate(String str, int startIndex) {
+        if (startIndex == str.length()-1) {
+            result.add(str);
+            return;
+        }
+
+        for(int i=startIndex; i<str.length(); i++) {
+            str = swap(str, startIndex, i);
+            enumerate(str, startIndex+1);
+            str = swap(str, startIndex, i); // backtracking
+        }
+    }
+
+    public static void main(String[] args) {
+        String str = "ABC";
+
+        BackTracking_StringPermutations permutations = new BackTracking_StringPermutations();
+        permutations.enumerate(str, 0);
+
+        System.out.println(permutations.result.stream().collect(Collectors.joining(" ")));
+    }
+}