Added solution to find largest sum subsequence and find smallest k

YogenRaii · YogenRaii · commit 21ea5982b642 · 2019-06-24T08:30:40.000-05:00
diff --git a/src/main/java/com/eprogrammerz/examples/algorithm/crackingCoding/ContinuousSequence.java b/src/main/java/com/eprogrammerz/examples/algorithm/crackingCoding/ContinuousSequence.java
@@ -0,0 +1,63 @@
+package com.eprogrammerz.examples.algorithm.crackingCoding;
+
+import org.junit.Test;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import static org.junit.Assert.assertArrayEquals;
+
+/**
+ * You are given an array of integers (both positive and negative). Find the contiguous sequence with the largest sum. Return the sum.
+ *
+ * EXAMPLE
+ * lnput:2, -8, 3, -2, 4, -10 Output:5 (i.e•, {3, -2, 4})
+ */
+public class ContinuousSequence {
+    /**
+     * [2, -8, 3, -2, 4, -10]
+     * sum arr: [2, -6, -3, -5, -1, -11]
+     * 2
+     * 3
+     * 4
+     */
+    /**
+     * O(n^2)
+     *
+     * @param arr
+     * @return
+     */
+    public int[] largestSumSeq(int[] arr) {
+        int sum = Integer.MIN_VALUE;
+
+        List<Integer> sequence = new ArrayList<>();
+
+        for (int i = 0; i < arr.length; i++) {
+            int tempSum = 0;
+            List<Integer> tempSeq = new ArrayList<>();
+            for (int j = i; j < arr.length; j++) {
+                tempSum += arr[j];
+                tempSeq.add(arr[j]);
+                if (tempSum > sum) {
+                    sum = tempSum;
+                    sequence.clear();
+                    sequence.addAll(tempSeq);
+                }
+            }
+        }
+
+        int[] result = new int[sequence.size()];
+        for (int i = 0; i < result.length; i++) {
+            result[i] = sequence.get(i);
+        }
+        return result;
+    }
+
+    @Test
+    public void testLargestSumSeq() {
+        int[] arr = new int[]{2, -8, 3, -2, 4, -10};
+        int[] actual = largestSumSeq(arr);
+        int[] expected = new int[]{3, -2, 4};
+        assertArrayEquals(expected, actual);
+    }
+}
diff --git a/src/main/java/com/eprogrammerz/examples/algorithm/crackingCoding/SmallestK.java b/src/main/java/com/eprogrammerz/examples/algorithm/crackingCoding/SmallestK.java
@@ -0,0 +1,45 @@
+package com.eprogrammerz.examples.algorithm.crackingCoding;
+
+import org.junit.Test;
+
+import java.util.*;
+
+import static org.junit.Assert.assertArrayEquals;
+
+/**
+ * Design an algorithm to find the smallest K numbers in an array.
+ */
+public class SmallestK {
+    public int[] findKSmallest(int[] arr, int k) {
+        // use max heap so that max of current will be on root
+        PriorityQueue<Integer> pq = new PriorityQueue<>((n1, n2) -> n2 - n1);
+
+        for (int i = 0; i < k; i++) { // O(k logk)
+            pq.add(arr[i]);
+        }
+
+        for (int i = k; i < arr.length; i++) {   // O(n logk)
+            if (!pq.isEmpty() && pq.peek() > arr[i]) {
+                pq.poll();
+                pq.add(arr[i]);
+            }
+        }
+
+        int[] result = new int[k];
+
+        int idx = 0;
+        for (int n : pq) {
+            result[idx++] = n;
+        }
+
+        return result;
+    }
+
+    @Test
+    public void testFindSmallestK() {
+        int[] input = new int[]{5, 1, 4, 3, 10, 6, 2};
+        int[] expected = new int[]{3, 1, 2};
+        int[] actual = findKSmallest(input, 3);
+        assertArrayEquals(expected, actual);
+    }
+}
