Create 1562-find-latest-group-of-size-m.js

Author: everthis

1562-find-latest-group-of-size-m.js

@@ -0,0 +1,80 @@
+/**
+ * @param {number[]} arr
+ * @param {number} m
+ * @return {number}
+ */
+const findLatestStep = function(arr, m) {
+    const uF = new UnionFind(arr);
+    const mRecords = new Set(); // This contains parents whose rank is m 
+    const visited = new Set();
+    let res = -1;
+
+    for (let i = 0; i < arr.length; i++) {
+        let val = arr[i];
+        visited.add(val);
+        
+        if (visited.has(val - 1)) {
+            let parent1 = uF.find(val);
+            let parent2 = uF.find(val - 1);
+			    // Since merging, the rank for val - 1 & val has changed,
+          // they are no longer m. Hence removed them from set.
+            mRecords.delete(parent1);  
+            mRecords.delete(parent2);
+            uF.union(val, val - 1);
+        }
+        
+        if (visited.has(val + 1)) {
+            let parent1 = uF.find(val);
+            let parent2 = uF.find(val + 1);
+            mRecords.delete(parent1);
+            mRecords.delete(parent2);
+            uF.union(val, val + 1);
+        }
+        
+        let parent = uF.find(val);
+        if (uF.ranks.get(parent) === m) mRecords.add(parent);
+        if (mRecords.size > 0) res = i + 1;  
+    }
+    
+    return res;  
+};
+
+class UnionFind {
+    constructor(arr) {
+        [this.parents, this.ranks] = this.initialise(arr);
+    }
+    
+    initialise(arr) {
+        const parents = new Map();
+        const ranks = new Map();
+        arr.forEach(val => {
+            parents.set(val, val);
+            ranks.set(val, 1);
+        })
+        
+        return [parents, ranks];
+    }
+    
+    find(val) {
+        if (this.parents.get(val) === val) return val;
+        this.parents.set(val, this.find(this.parents.get(val)));
+        return this.parents.get(val);
+    }
+    
+    union(m, n) {
+        const rootM = this.find(m);
+        const rootN = this.find(n);
+        
+        if (rootM === rootN) return;
+        if (rootM > rootN) {
+            this.updateParent(rootN, rootM);
+        } else {
+            this.updateParent(rootM, rootN);
+        }
+    }
+    
+    updateParent(child, parent) {
+        this.ranks.set(parent, this.ranks.get(parent) + this.ranks.get(child));
+        this.parents.set(child, parent);
+    }
+}