Create 2597-the-number-of-beautiful-subsets.js

javascript/2597-the-number-of-beautiful-subsets.js

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+/**
+ * BackTracking | Hashing | Recursion
+ * Time O(2^n * n) | Space O(n)
+ * https://leetcode.com/problems/the-number-of-beautiful-subsets
+ * @param {number[]} nums
+ * @param {number} k
+ * @return {number}
+ */
+var beautifulSubsets = function(nums, k) {
+
+    const numSet = {};
+
+    const checkIfValid = (arr) => {
+        if (!arr.length) return false;
+        for( let i = 0; i < arr.length; i++) {
+            const key0 = arr[i] - k;
+            const key1 = arr[i] + k;
+
+            if (numSet[key0]) return false;
+            if (numSet[key1]) return false;
+        }
+        return true;
+    }
+
+    const addToNumSet = (key) => {
+        numSet[key] = (numSet[key] && numSet[key] + 1) || 1;
+    }
+
+    const removeFromNumSet = (key) => {
+        numSet[key] -= 1;
+    }
+
+    let result = 0;
+    const dfs = (arr, i) => {
+        if (i === nums.length) {
+            if (checkIfValid(arr)) result++;
+            return;
+        }
+
+        // we have 2 choices.
+        arr.push(nums[i]);
+        addToNumSet(nums[i]);
+        dfs(arr, i+1);
+        arr.pop(nums[i]);
+        removeFromNumSet(nums[i]);
+        dfs(arr, i+1);
+    }
+
+    dfs([],0);
+    return result;
+};