Cedar-Bailey

lib/exercises.js

@@ -1,17 +1,67 @@
 // This method will return an array of arrays.
 // Each subarray will have strings which are anagrams of each other
-// Time Complexity: ?
-// Space Complexity: ?
+// Time Complexity: O(n*m)
+// Space Complexity: O(n+n) -> O(n)
 function groupedAnagrams(strings) {
-    throw new Error("Method hasn't been implemented yet!");
+    let freqMap = new Map();
+
+    let result = [];
+    for (let word of strings) {
+        let count = new Array(26).fill(0);
+        for (let char of word) {
+            count[char.charCodeAt(0) - 97] += 1;
+        }
+
+        if (freqMap.get(count.toString())) {
+            freqMap.get(count.toString()).push(word);
+        } else {
+            freqMap.set(count.toString(), [word]);
+        }
+    }
+
+    for (let list of freqMap.values()) {
+        result.push(list);
+    }
+    return result;
 }
 
 // This method will return the k most common elements
 // in the case of a tie it will select the first occuring element.
-// Time Complexity: ?
-// Space Complexity: ?
+// Time Complexity: O(n)
+// Space Complexity: O(n+n+n) -> O(n)
 function topKFrequentElements(list, k) {
-    throw new Error("Method hasn't been implemented yet!");
+
+    let counts = new Map();
+    let buckets = [];
+    for (let i = 0; i <= list.length; i++)
+        buckets.push([]);
+
+    // count frequent of the elements
+    for (let num of list) {
+        if (counts.has(num)) {
+            counts.set(num, counts.get(num) + 1);
+        } else {
+            counts.set(num, 1);
+        }
+    } 
+    // put them into buckets by frequent
+    for (let [key, value] of counts) {
+        buckets[value].push(key);
+    }
+
+    // fetch the larget frequest bucket first, until reach k
+    let ans = [];
+    for (let i = buckets.length - 1; i > 0 && ans.length < k; i--) {
+        if (buckets[i].length !== 0) ans.push(...buckets[i]);
+    }
+
+    if (ans.length > k) {
+        while (ans.length !== k) {
+            ans.pop();
+        }
+    }
+
+    return ans;
 }
 
 
@@ -20,10 +70,55 @@ function topKFrequentElements(list, k) {
 //   Each element can either be a ".", or a digit 1-9
 //   The same digit cannot appear twice or more in the same 
 //   row, column or 3x3 subgrid
-// Time Complexity: ?
-// Space Complexity: ?
-function validSudoku(table) {
-    throw new Error("Method hasn't been implemented yet!");
+// Time Complexity: O(n^2) -> O(1) because of fixed board size
+// Space Complexity: O(n^2) -> O(1) because of fixed board size
+function validSudoku(board) {
+    let store = {
+        rows: {},
+        cols: {},
+        square: {},
+      };
+    for (let i = 0; i < 9; i++) {
+        for (let j = 0; j < 9; j++) {
+          const box = board[i][j];
+
+          if (!store["rows"][i] && box !== ".") {
+            store["rows"][i] = [];
+            store["rows"][i].push(box);
+          } else if (box !== "." && !store["rows"][i].includes(box)) {
+            store["rows"][i].push(box);
+          } else if (store["rows"][i] && store["rows"][i].includes(box)) {
+            return false;
+          }
+
+          if (!store["cols"][j] && box !== ".") {
+            store["cols"][j] = [];
+            store["cols"][j].push(box);
+          } else if (box !== "." && !store["cols"][j].includes(box)) {
+            store["cols"][j].push(box);
+          } else if (store["cols"][j] && store["cols"][j].includes(box)) {
+            return false;
+          }
+
+          const squareRowId = Math.ceil((i + 1) / 3);
+          const squareColId = Math.ceil((j + 1) / 3);
+          const squareId = `${squareRowId}-${squareColId}`;
+
+          if (!store["square"][squareId] && box !== ".") {
+            store["square"][squareId] = [];
+            store["square"][squareId].push(box);
+          } else if (box !== "." && !store["square"][squareId].includes(box)) {
+            store["square"][squareId].push(box);
+          } else if (
+            store["square"][squareId] &&
+            store["square"][squareId].includes(box)
+          ) {
+            return false;
+          }
+        }
+      }
+      return true;
+
 }
 
 module.exports = {