3351. Sum of Good Subsequences

Author: sergeyleschev

3001-3500/3351. Sum of Good Subsequences.ts

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+// Solution by Sergey Leschev
+// 3351. Sum of Good Subsequences
+// DP
+
+function sumOfGoodSubsequences(nums: number[]): number {
+    const MOD = 1000000007
+
+    const count: Map<number, number> = new Map()
+    const sum: Map<number, number> = new Map()
+
+    for (const num of nums) {
+        const cntPrev = count.get(num - 1) || 0
+        const cntCurr = count.get(num) || 0
+        const cntNext = count.get(num + 1) || 0
+
+        const sumPrev = sum.get(num - 1) || 0
+        const sumCurr = sum.get(num) || 0
+        const sumNext = sum.get(num + 1) || 0
+
+        count.set(num, (cntPrev + cntNext + cntCurr + 1) % MOD)
+
+        const newSum = (sumPrev + sumNext + sumCurr + num * (cntPrev + cntNext + 1)) % MOD
+        sum.set(num, newSum)
+    }
+
+    let result = 0
+    for (const value of sum.values()) {
+        result = (result + value) % MOD
+    }
+
+    return result
+}