add flood fill and course schedule

Author: beck chen

Leetcode Visuals/Trees and Graphs.drawio

@@ -0,0 +1,48 @@
+var canFinish = function (numCourses, prerequisites) {
+    const courseToPrereqMap = {};
+    const isOnCurrentPath = {};
+    const isVisited = {};
+
+    for (let ii = 0; ii < prerequisites.length; ii++) {
+        const [course, prereq] = prerequisites[ii];
+        courseToPrereqMap[course] = !courseToPrereqMap[course] ? [prereq] : [...courseToPrereqMap[course], prereq]
+    }
+
+    const courseNums = Object.keys(courseToPrereqMap);
+    for (let ii = 0; ii < courseNums.length; ii++) {
+        const courseNum = courseNums[ii];
+        if (hasCycle(courseNum)) {
+            return false;
+        }
+    }
+
+    function hasCycle(courseNum) {
+        if (isOnCurrentPath[courseNum]) {
+            return true;
+        }
+
+        if (isVisited[courseNum]) {
+            return false;
+        }
+
+        if (!courseToPrereqMap[courseNum] || courseToPrereqMap[courseNum].length === 0) {
+            return false;
+        }
+
+        isOnCurrentPath[courseNum] = true;
+        const prereqs = courseToPrereqMap[courseNum];
+        for (let ii = 0; ii < prereqs.length; ii++) {
+            const prereqNum = prereqs[ii];
+            if (hasCycle(prereqNum)) {
+                return true;
+            }
+        }
+
+        isOnCurrentPath[courseNum] = false;
+        isVisited[courseNum] = true;
+
+        return false;
+    }
+
+    return true;
+}

leetcode practice/trees and graphs/courseSchedule.js

@@ -0,0 +1,26 @@
+/**
+ * @param {number[][]} image
+ * @param {number} sr
+ * @param {number} sc
+ * @param {number} newColor
+ * @return {number[][]}
+ */
+
+var floodFill = function (image, sr, sc, newColor) {
+    function traverse(image, rowIndex, colIndex, oldColor, newColor) {
+        const indexOOB = rowIndex < 0 || colIndex < 0 || rowIndex >= image.length || colIndex >= image[0].length;
+        if (indexOOB || image[rowIndex][colIndex] !== oldColor || image[rowIndex][colIndex] === newColor) {
+            return;
+        }
+
+        image[rowIndex][colIndex] = newColor;
+        traverse(image, rowIndex + 1, colIndex, oldColor, newColor);
+        traverse(image, rowIndex - 1, colIndex, oldColor, newColor);
+        traverse(image, rowIndex, colIndex + 1, oldColor, newColor);
+        traverse(image, rowIndex, colIndex - 1, oldColor, newColor);
+    }
+
+    const oldColor = image[sr][sc];
+    traverse(image, sr, sc, oldColor, newColor);
+    return image;
+}