Added solution for combination sum to target and kth permutation

YogenRaii · YogenRaii · commit a2ab9dc1ba18 · 2019-06-30T09:36:10.000-05:00
diff --git a/src/main/java/com/eprogrammerz/examples/algorithm/interviewbit/CombinationII.java b/src/main/java/com/eprogrammerz/examples/algorithm/interviewbit/CombinationII.java
@@ -0,0 +1,44 @@
+package com.eprogrammerz.examples.algorithm.interviewbit;
+
+import org.junit.Test;
+
+import java.util.*;
+
+import static org.junit.Assert.assertEquals;
+
+/**
+ * find all combinations of numbers sum to the target
+ */
+public class CombinationII {
+    List<List<Integer>> combinations(List<Integer> list, int target) {
+        List<List<Integer>> comb = new ArrayList<>();
+        Collections.sort(list);
+        combinations(list, comb, new ArrayList<>(), target, 0);
+        return comb;
+    }
+
+    private void combinations(List<Integer> list, List<List<Integer>> comb, List<Integer> temp, int target, int start) {
+        if (target == 0) {
+            comb.add(new ArrayList<>(temp));
+            return;
+        }
+        for (int i = start; i < list.size() && target >= list.get(i); i++) {
+            if (i != start && list.get(i - 1).equals(list.get(i))) continue;
+            temp.add(list.get(i));
+
+            combinations(list, comb, temp, target - list.get(i), i + 1);
+            temp.remove(temp.size() - 1);
+        }
+    }
+
+    @Test
+    public void test() {
+        List<Integer> input = Arrays.asList(10, 1, 2, 7, 3, 4, 1, 2);
+        List<List<Integer>> actual = combinations(input, 8);
+
+        List<List<Integer>> expected = Arrays.asList(Arrays.asList(1, 1, 2, 4),
+                Arrays.asList(1, 2, 2, 3), Arrays.asList(1, 3, 4), Arrays.asList(1, 7),
+                Arrays.asList(2, 2, 4));
+        assertEquals(expected, actual);
+    }
+}
diff --git a/src/main/java/com/eprogrammerz/examples/algorithm/interviewbit/KthPermutation.java b/src/main/java/com/eprogrammerz/examples/algorithm/interviewbit/KthPermutation.java
@@ -0,0 +1,91 @@
+package com.eprogrammerz.examples.algorithm.interviewbit;
+
+import org.junit.Test;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import static org.junit.Assert.assertEquals;
+
+/**
+ * Given n, 1.. n and k, find permutation of n numbers at kth position
+ */
+public class KthPermutation {
+    public String getPermutation(int n, int k) {
+        List<Integer> num = new ArrayList<>();
+        for (int i = 1; i <= n; i++) {
+            num.add(i);
+        }
+        List<List<Integer>> per = new ArrayList<>();
+        permutate(num, k, per, new ArrayList<>());
+        List<Integer> p = per.get(per.size() - 1);
+        StringBuilder res = new StringBuilder();
+        for (int i : p) {
+            res.append(i);
+        }
+        return res.toString();
+    }
+
+    private void permutate(List<Integer> num, int k, List<List<Integer>> per,
+                           List<Integer> temp) {
+        if (per.size() == k) return;
+
+        if (num.size() == 0) {
+            per.add(new ArrayList<>(temp));
+        } else {
+            for (int i = 0; i < num.size(); i++) {
+                List<Integer> r1 = num.subList(0, i);
+                List<Integer> r2 = num.subList(i + 1, num.size());
+
+                List<Integer> r = new ArrayList<>();
+                r.addAll(r1);
+                r.addAll(r2);
+
+                temp.add(num.get(i));
+                permutate(r, k, per, temp);
+                temp.remove(num.get(i));
+            }
+        }
+    }
+
+    @Test
+    public void testKthPermutation() {
+        String kth = getPermutation(3, 4);
+        assertEquals("231", kth);
+    }
+
+    public String getKthPermutation(int n, int k) {
+        List<Integer> num = new ArrayList<>();
+        for (int i = 1; i <= n; i++) {
+            num.add(i);
+        }
+
+        return getKthPermutation(num, k - 1);
+    }
+
+    private String getKthPermutation(List<Integer> num, int k) {
+        int size = num.size();
+        if (size == 0) return "";
+
+        if (k > fact(size)) return "";
+
+        int f = fact(size - 1);
+
+        int pos = k / f;
+
+        k = k % f;
+
+        return String.valueOf(num.remove(pos)) + getKthPermutation(num, k);
+    }
+
+    private int fact(int n) {
+        if (n == 0 || n == 1) return 1;
+        return n * fact(n - 1);
+    }
+
+    @Test
+    public void testKthPermutationBetter() {
+        String kth = getKthPermutation(3, 4);
+        assertEquals("231", kth);
+    }
+}
