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

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]
}