go: add «241. Different Ways to Add Parentheses»

Signed-off-by: Matej Focko <me@mfocko.xyz>

go/different-ways-to-add-parentheses.go

@@ -0,0 +1,66 @@
+package main
+
+import (
+	"unicode"
+)
+
+func diffWaysToCompute(expression string) []int {
+	n := len(expression)
+	dp := make([][][]int, n)
+	for i := range dp {
+		dp[i] = make([][]int, n)
+	}
+
+	computeBase := func() {
+		for i, c := range expression {
+			if !unicode.IsDigit(c) {
+				continue
+			}
+
+			digit := int(c - '0')
+			dp[i][i] = append(dp[i][i], digit)
+
+			if i+1 < n && unicode.IsDigit(rune(expression[i+1])) {
+				nextDigit := int(expression[i+1] - '0')
+				dp[i][i+1] = append(dp[i][i+1], digit*10+nextDigit)
+			}
+		}
+	}
+	computeBase()
+
+	precompute := func(op byte, left, right, results []int) []int {
+		for _, l := range left {
+			for _, r := range right {
+				switch op {
+				case '+':
+					results = append(results, l+r)
+				case '-':
+					results = append(results, l-r)
+				case '*':
+					results = append(results, l*r)
+				}
+			}
+		}
+
+		return results
+	}
+	computeSubexpression := func(l, r int) {
+		for mid := l; mid <= r; mid++ {
+			if unicode.IsDigit(rune(expression[mid])) {
+				continue
+			}
+
+			left, right := dp[l][mid-1], dp[mid+1][r]
+			dp[l][r] = precompute(expression[mid], left, right, dp[l][r])
+		}
+	}
+
+	for length := 3; length <= n; length++ {
+		for l := 0; l+length-1 < n; l++ {
+			r := l + length - 1
+			computeSubexpression(l, r)
+		}
+	}
+
+	return dp[0][n-1]
+}