Add solution #403

Author: JoshCrozier

README.md

@@ -321,6 +321,7 @@
 400|[Nth Digit](./0400-nth-digit.js)|Medium|
 401|[Binary Watch](./0401-binary-watch.js)|Easy|
 402|[Remove K Digits](./0402-remove-k-digits.js)|Medium|
+403|[Frog Jump](./0403-frog-jump.js)|Hard|
 404|[Sum of Left Leaves](./0404-sum-of-left-leaves.js)|Easy|
 405|[Convert a Number to Hexadecimal](./0405-convert-a-number-to-hexadecimal.js)|Easy|
 407|[Trapping Rain Water II](./0407-trapping-rain-water-ii.js)|Hard|

solutions/0403-frog-jump.js

@@ -0,0 +1,39 @@
+/**
+ * 403. Frog Jump
+ * https://leetcode.com/problems/frog-jump/
+ * Difficulty: Hard
+ *
+ * A frog is crossing a river. The river is divided into some number of units, and at each
+ * unit, there may or may not exist a stone. The frog can jump on a stone, but it must not
+ * jump into the water.
+ *
+ * Given a list of stones positions (in units) in sorted ascending order, determine if the
+ * frog can cross the river by landing on the last stone. Initially, the frog is on the
+ * first stone and assumes the first jump must be 1 unit.
+ *
+ * If the frog's last jump was k units, its next jump must be either k - 1, k, or k + 1
+ * units. The frog can only jump in the forward direction.
+ */
+
+/**
+ * @param {number[]} stones
+ * @return {boolean}
+ */
+var canCross = function(stones) {
+  const dp = new Map();
+  stones.forEach(stone => dp.set(stone, new Set()));
+  dp.get(0).add(0);
+
+  for (let i = 0; i < stones.length; i++) {
+    const curr = stones[i];
+    for (const prevJump of dp.get(curr)) {
+      for (const jump of [prevJump - 1, prevJump, prevJump + 1]) {
+        if (jump > 0 && dp.has(curr + jump)) {
+          dp.get(curr + jump).add(jump);
+        }
+      }
+    }
+  }
+
+  return dp.get(stones[stones.length - 1]).size > 0;
+};