Create 1377-frog-position-after-t-seconds.js

Author: everthis

1377-frog-position-after-t-seconds.js

@@ -0,0 +1,42 @@
+/**
+ * @param {number} n
+ * @param {number[][]} edges
+ * @param {number} t
+ * @param {number} target
+ * @return {number}
+ */
+const frogPosition = function (n, edges, t, target) {
+  const graph = { 1: new Set() }
+  for (let [from, to] of edges) {
+    if (graph[from]) graph[from].add(to)
+    else graph[from] = new Set([to])
+    if (graph[to]) graph[to].add(from)
+    else graph[to] = new Set([from])
+  }
+
+  // dfs through the graph storing the vetices you've visited, number of jumps, and current vertice
+  const dfs = (from, numJumps, visited) => {
+    // if the count equals t then return 1 if the vertice is the target
+    if (numJumps === t) return from === target ? 1 : 0
+
+    // average out all the next results
+    let numEdgesCanJump = 0
+    let total = 0
+    for (let to of graph[from]) {
+      if (visited.has(to)) continue
+      visited.add(to)
+      total += dfs(to, numJumps + 1, visited)
+      visited.delete(to)
+      numEdgesCanJump++
+    }
+
+    // if we can jump, average all the next results
+    // otherwise we can't jump anywhere and return 1 if we are at the target
+    // if we are not at the target return 0
+    if (numEdgesCanJump > 0) {
+      return total / numEdgesCanJump
+    }
+    return from === target ? 1 : 0
+  }
+  return dfs(1, 0, new Set([1]))
+}