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refactor 377
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‎README.md‎

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@@ -252,7 +252,7 @@ Your ideas/fixes/algorithms are more than welcome!
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|380|[Insert Delete GetRandom O(1)](https://leetcode.com/problems/insert-delete-getrandom-o1/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_380.java)| O(n) | O(1)| Medium| Design, HashMap
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|379|[Design Phone Directory](https://leetcode.com/problems/design-phone-directory/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_379.java)| O(1)|O(n) | Medium|
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|378|[Kth Smallest Element in a Sorted Matrix](https://leetcode.com/problems/kth-smallest-element-in-a-sorted-matrix/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_378.java)| O(logm*n) | O(1)| Medium| Binary Search
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|377|[Combination Sum IV](https://leetcode.com/problems/combination-sum-iv/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_377.java)| O(?)|O(?) | Medium|
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|377|[Combination Sum IV](https://leetcode.com/problems/combination-sum-iv/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_377.java)| O(n^2)|O(n) | Medium| DP
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|376|[Wiggle Subsequence](https://leetcode.com/problems/wiggle-subsequence/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_376.java)| O(n)|O(1) | Medium| DP, Greedy
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|375|[Guess Number Higher or Lower II](https://leetcode.com/problems/guess-number-higher-or-lower-ii/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_375.java)| O(n^2)|O(n^2) | Medium| DP
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|374|[Guess Number Higher or Lower](https://leetcode.com/problems/guess-number-higher-or-lower/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_374.java)| O(logn)|O(1) | Easy| Binary Search

‎src/main/java/com/fishercoder/solutions/_377.java‎

Lines changed: 78 additions & 41 deletions
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@@ -1,11 +1,12 @@
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package com.fishercoder.solutions;
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import com.fishercoder.common.utils.CommonUtils;
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import java.util.ArrayList;
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import java.util.Arrays;
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import java.util.List;
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/**Given an integer array with all positive numbers and no duplicates,
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/**
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* 377. Combination Sum IV
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* Given an integer array with all positive numbers and no duplicates,
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* find the number of possible combinations that add up to a positive integer target.
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Example:
@@ -29,54 +30,90 @@
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Follow up:
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What if negative numbers are allowed in the given array?
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How does it change the problem?
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What limitation we need to add to the question to allow negative numbers?*/
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What limitation we need to add to the question to allow negative numbers?
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*/
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public class _377 {
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/**since this question doesn't require to return all the combination result, instead, it just wants one number, we could use DP
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the idea is similar to Climbing Stairs.
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adopted this solution: https://discuss.leetcode.com/topic/52186/my-3ms-java-dp-solution*/
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public int combinationSum4(int[] nums, int target) {
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Arrays.sort(nums);
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int[] result = new int[target + 1];
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for (int i = 1; i < result.length; i++) {
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for (int n : nums) {
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if (n > target) {
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break;
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} else if (n == target) {
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result[i]++;
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} else {
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result[i] += result[i - n];
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public static class Solution1 {
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/**
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* this normal backtracking recursive solution will end up in MLE by this testcase: [4,2,1], 32
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*/
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public int combinationSum4(int[] nums, int target) {
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List<List<Integer>> result = new ArrayList();
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Arrays.sort(nums);
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backtracking(nums, target, new ArrayList(), result);
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return result.size();
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}
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private void backtracking(int[] nums, int target, List<Integer> list,
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List<List<Integer>> result) {
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if (target == 0) {
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result.add(new ArrayList(list));
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} else if (target > 0) {
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for (int i = 0; i < nums.length; i++) {
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list.add(nums[i]);
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backtracking(nums, target - nums[i], list, result);
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list.remove(list.size() - 1);
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}
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}
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}
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return result[target];
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}
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//this normal backtracking recursive solution will end up in TLE.
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public List<List<Integer>> combinationSum4_printout(int[] nums, int target) {
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List<List<Integer>> result = new ArrayList();
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Arrays.sort(nums);
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backtracking(0, nums, target, new ArrayList(), result);
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return result;
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}
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public static class Solution2 {
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/**
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* Since we don't need to get all of the combinations, instead,
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* we only need to get the possible count, I can use only a count instead of "List<List<Integer>> result"
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* However, it also ended up in TLE by this testcase: [1,2,3], 32
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*/
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public static int count = 0;
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public int combinationSum4(int[] nums, int target) {
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Arrays.sort(nums);
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backtracking(nums, target, new ArrayList());
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return count;
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}
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private void backtracking(int start, int[] nums, int target, ArrayList temp,
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List<List<Integer>> result) {
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if (target == 0) {
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List<Integer> newTemp = new ArrayList(temp);
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result.add(newTemp);
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} else if (target > 0) {
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for (int i = start; i < nums.length; i++) {
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temp.add(nums[i]);
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backtracking(i, nums, target - nums[i], temp, result);
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temp.remove(temp.size() - 1);
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private void backtracking(int[] nums, int target, List<Integer> list) {
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if (target == 0) {
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count++;
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} else if (target > 0) {
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for (int i = 0; i < nums.length; i++) {
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list.add(nums[i]);
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backtracking(nums, target - nums[i], list);
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list.remove(list.size() - 1);
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}
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}
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}
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}
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public static void main(String... strings) {
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_377 test = new _377();
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int[] nums = new int[]{1, 2, 3};
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int target = 4;
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CommonUtils.printListList(test.combinationSum4_printout(nums, target));
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public static class Solution3 {
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/**
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* Since this question doesn't require to return all the combination result, instead, it just wants one number, we could use DP
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* the idea is similar to Climbing Stairs.
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*
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* The idea is very clear as the code speaks for itself:
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* It's easy to find the routine
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* dp[0] = 0;
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* dp[1] = 1;
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* ...
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*
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* Reference: https://discuss.leetcode.com/topic/52186/my-3ms-java-dp-solution
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*/
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public int combinationSum4(int[] nums, int target) {
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Arrays.sort(nums);
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int[] result = new int[target + 1];
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for (int i = 1; i < result.length; i++) {
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for (int num : nums) {
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if (num > i) {
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break;
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} else if (num == i) {
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result[i]++;
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} else {
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result[i] += result[i - num];
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}
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}
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}
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return result[target];
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}
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}
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}

‎src/test/java/com/fishercoder/_377Test.java‎

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package com.fishercoder;
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import com.fishercoder.solutions._377;
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import org.junit.BeforeClass;
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import org.junit.Test;
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import static junit.framework.Assert.assertEquals;
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public class _377Test {
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private static _377.Solution1 solution1;
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private static _377.Solution2 solution2;
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private static _377.Solution3 solution3;
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private static int[] nums;
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private static int target;
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@BeforeClass
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public static void setup() {
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solution1 = new _377.Solution1();
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solution2 = new _377.Solution2();
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solution3 = new _377.Solution3();
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}
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@Test
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public void test1() {
25+
nums = new int[]{1,2,3};
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target = 4;
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assertEquals(7, solution1.combinationSum4(nums, target));
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assertEquals(7, solution2.combinationSum4(nums, target));
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assertEquals(7, solution3.combinationSum4(nums, target));
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}
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@Test
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public void test2() {
34+
nums = new int[]{4,2,1};
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target = 32;
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// assertEquals(39882198, solution1.combinationSum4(nums, target));//this results in MLE, so comment out
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solution2.count = 0;//always have to reset this global variable to be zero before using it again
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assertEquals(39882198, solution2.combinationSum4(nums, target));
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assertEquals(39882198, solution3.combinationSum4(nums, target));
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}
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}

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