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Commit c2b22e4

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Update solution for Subarray Sum Equals K
1 parent 7fc1579 commit c2b22e4

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2 files changed

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-44
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2 files changed

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‎README.md‎

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@@ -101,6 +101,7 @@ Algorithm exercises from LeetCode implemented in Java v11.
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### Prefix Sum
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- Product of the Last K Numbers | [Problem](https://leetcode.com/problems/product-of-the-last-k-numbers) | [Solution](src/solutions/ProductOfNumbers.java)
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- Substrings That Begin and End With the Same Letter | [Problem](https://leetcode.com/problems/substrings-that-begin-and-end-with-the-same-letter) | [Solution](src/solutions/SubstringsWithSameLetter.java)
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- Subarray Sum Equals K | [Problem](https://leetcode.com/problems/subarray-sum-equals-k) | [Solution](src/solutions/SubarraySumEqualsK.java)
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### Recursion
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- Closest Binary Search Tree Value | [Problem](https://leetcode.com/problems/closest-binary-search-tree-value)

‎src/solutions/SubarraySumEqualsK.java‎

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@@ -3,10 +3,26 @@
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import java.util.HashMap;
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import java.util.Map;
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// [Problem] https://leetcode.com/problems/subarray-sum-equals-k/
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// [Problem] https://leetcode.com/problems/subarray-sum-equals-k
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class SubarraySumEqualsK {
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// Hashmap storing prefix sum
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// O(n) time, O(n) space
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public int subarraySum(int[] nums, int k) {
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int count = 0, sum = 0;
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Map<Integer, Integer> sumCounts = new HashMap<>();
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sumCounts.put(0, 1);
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for (int num : nums) {
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sum += num;
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if (sumCounts.containsKey(sum - k)) {
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count += sumCounts.get(sum - k);
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}
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int sumCount = sumCounts.getOrDefault(sum, 0);
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sumCounts.put(sum, sumCount + 1);
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}
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return count;
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}
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// test
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// Test
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public static void main(String[] args) {
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SubarraySumEqualsK solution = new SubarraySumEqualsK();
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@@ -17,46 +33,4 @@ public static void main(String[] args) {
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System.out.println("Test passed? " + (expectedOutput == actualOutput));
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}
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// Using cumulative sum array - O(n^2) time, O(n) space
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public int subarraySumWithArray(int[] nums, int k) {
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int result = 0;
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int n = nums.length;
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int sum = 0;
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int[] sums = new int[n + 1];
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for (int i = 1; i <= n; i++) {
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sum += nums[i - 1];
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sums[i] = sum;
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}
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for (int i = 0; i < n; i++) {
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for (int j = i + 1; j < n + 1; j++) {
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if (sums[j] - sums[i] == k) {
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result++;
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}
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}
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}
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return result;
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}
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// Using cumulative sum hashmap - O(n) time, O(n) space
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public int subarraySum(int[] nums, int k) {
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int result = 0;
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Map<Integer, Integer> sumCounts = new HashMap<>();
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sumCounts.put(0, 1);
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int sum = 0;
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for (int num : nums) {
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sum += num;
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if (sumCounts.containsKey(sum - k)) {
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result += sumCounts.get(sum - k);
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}
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sumCounts.put(sum, sumCounts.getOrDefault(sum, 0) + 1);
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}
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return result;
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}
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}

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