Update 2801-count-stepping-numbers-in-range.js

Author: everthis

2801-count-stepping-numbers-in-range.js

@@ -1,3 +1,79 @@
+/**
+ * @param {string} low
+ * @param {string} high
+ * @return {number}
+ */
+var countSteppingNumbers = function (low, high) {
+  const mod = 1000000007
+  let init = () => new Array(101)
+    .fill(null)
+    .map(() =>
+      new Array(2)
+        .fill(null)
+        .map(() => new Array(2).fill(null).map(() => new Array(11).fill(-1))),
+    )
+//   console.log(dp)
+  const helper = (pos, tight, isZero, prevDigit, s) => {
+    if (pos === s.length) {
+      if (isZero) return 0
+      return 1
+    }
+
+    if (dp[pos][tight][isZero][prevDigit + 1] !== -1)
+      return dp[pos][tight][isZero][prevDigit + 1]
+
+    let res = 0
+    let limit
+
+    if (tight) limit = parseInt(s[pos])
+    else limit = 9
+
+    for (let curDigit = 0; curDigit <= limit; curDigit++) {
+      let newTight = tight
+      if (tight && curDigit < limit) newTight = 0
+
+      let willBeZero = isZero
+      if (isZero && curDigit > 0) willBeZero = 0
+
+      if (isZero) {
+        res += helper(pos + 1, newTight, willBeZero, curDigit, s)
+        res %= mod
+      } else {
+        if (Math.abs(curDigit - prevDigit) === 1) {
+          res += helper(pos + 1, newTight, willBeZero, curDigit, s)
+          res %= mod
+        }
+      }
+    }
+
+    dp[pos][tight][isZero][prevDigit + 1] = res
+    return res
+  }
+  let dp = init()
+  let l = helper(0, 1, 1, -1, low)
+
+  dp = init()
+  let r = helper(0, 1, 1, -1, high)
+
+  let res = r - l
+  res = (res + mod) % mod
+
+  let add = true
+  for (let i = 1; i < low.length; i++) {
+    if (Math.abs(low[i] - low[i - 1]) !== 1) {
+      add = false
+      break
+    }
+  }
+  if (add) res++
+
+  res %= mod
+  return res
+}
+
+// another
+
+
 const minus_mod = (x, y, mod) => ((x - y) % mod + mod) % mod;
 const mod = 1e9 + 7, ll = BigInt;
 let memo;