Add solution

Author: Annahcj

Counting/1394.find-lucky-integer-in-an-array.js

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+// 1394. Find Lucky Integer in an Array
+// Given an array of integers arr, a lucky integer is an integer that has a frequency in the array equal to its value.
+// Return the largest lucky integer in the array. If there is no lucky integer return -1.
+
+
+// Solution: Counting
+
+// Count the occurrances of each number and store it in a hashmap.
+// Go through each entry in the hashmap and record the maximum number which is equal to its frequency.
+
+// Time Complexity: O(n) 1ms
+// Space Complexity: O(n) 56MB
+function findLucky(arr) {
+  const count = {};
+  for (let num of arr) {
+    count[num] = (count[num] || 0) + 1;
+  }
+  let max = -1;
+  for (let num in count) {
+    if (num == count[num]) {
+      max = Math.max(max, Number(num));
+    }
+  }
+  return max;
+};
+
+// Two test cases
+console.log(findLucky([2,2,3,4])) // 2
+console.log(findLucky([1,2,2,3,3,3])) // 3