leetcode(45-jump-game-ii): working solution

Author: uldissturms

leetcode/45-jump-game-ii.test.js

@@ -9,6 +9,7 @@ test('solves jump list', t => {
 
 test('solves jump list - with zero as value', t => {
   t.is(solve([2, 3, 1, 0, 4]), 2)
+  t.is(solve([1, 2, 0, 1]), 2) // 60th test case
 })
 
 test('solves jump list - empty list', t => {
@@ -25,27 +26,81 @@ test('solves jump list - two items', t => {
   t.is(solve([2, 1]), 1)
 })
 
+test('multiple ones', t => {
+  t.is(solve([1, 2, 1, 1, 1]), 3) // 65th test case
+})
+
 test('solves jump list - large list', t => {
   const size = 50000
   t.is(solve(new Array(size).fill(1)), size - 1)
 })
 
-test.skip('solves jump list - large descending list', t => {
+test('solves jump list - large descending list', t => {
   const size = 25000
   const input = new Array(size).fill(1).map((_, idx) => size - idx)
   t.is(solve(input), 1)
 })
 
-test.skip('solves jump list - large descending list twice', t => {
+test('solves jump list - large descending list twice', t => {
   const size = 25000
   const list = new Array(size).fill(1).map((_, idx) => size - idx)
   t.is(solve(list.concat(list)), 2)
 })
 
+test('solves jump list - value greater than prev', t => {
+  t.is(solve([4, 3, 1]), 1)
+  t.is(solve([4, 1, 3, 1]), 1)
+})
+
+test('solves jump list - value less than prev', t => {
+  t.is(solve([2, 4, 2]), 1)
+  t.is(solve([4, 5, 2, 4, 2]), 1)
+})
+
 const solve = (jumps) =>
-  solveI(jumps)
+  solveI2(jumps)
+  // solveI(jumps)
   // solveR(jumps)[0]
 
+const solveI2 = (jumps) => {
+  const len = jumps.length
+  if (len <= 1) {
+    return 0
+  }
+
+  const map = new Array(jumps.length).fill(0).map((_, idx) => ([Infinity, idx]))
+  map[len - 1] = [0, 0]
+
+  for (let idx = len - 2; idx >= 0; idx--) {
+    const curJumps = jumps[idx]
+
+    // deadend - leave as infinity
+    if (curJumps === 0) {
+      map[idx] = [Infinity, 0]
+      continue
+    }
+
+    const [prevC, prevUsed] = map[idx + 1]
+    let [bestC, bestUsed] = [prevC + 1, 1] // zero case to be handled later
+    const diff = curJumps - prevUsed
+    const prevEnd = idx + prevUsed + 1
+
+    if (diff > 0) {
+      for (let pos = prevEnd; pos < Math.min(prevEnd + diff, len); pos++) {
+        const [candidateC] = map[pos]
+        if (candidateC + 1 < bestC) {
+          bestC = candidateC + 1
+          bestUsed = pos - idx
+        }
+      }
+    }
+
+    map[idx] = [bestC, bestUsed]
+  }
+
+  return map[0][0]
+}
+
 const solveI = (jumps) => {
   const len = jumps.length
   if (len <= 1) {