1031 done

Author: aQuaYi

Algorithms/1031.maximum-sum-of-two-non-overlapping-subarrays/maximum-sum-of-two-non-overlapping-subarrays.go

@@ -1,57 +1,21 @@
 package problem1031
 
-import "sort"
+// ref: https://leetcode.com/problems/maximum-sum-of-two-non-overlapping-subarrays/discuss/278251/JavaC%2B%2BPython-O(N)Time-O(1)-Space
 
 func maxSumTwoNoOverlap(A []int, L int, M int) int {
-	ls, ms := sums(A, L), sums(A, M)
-	lSize, mSize := len(ls), len(ms)
-	res := 0
-	for i := 0; i < lSize; i++ {
-		if ls[i].sum+ms[0].sum <= res {
-			break
-		}
-		j := 0
-		for j < mSize && ls[i].isOverlapping(ms[j]) {
-			j++
-		}
-		if j < mSize {
-			res = max(res, ls[i].sum+ms[j].sum)
-		}
+	for i := 1; i < len(A); i++ {
+		A[i] += A[i-1]
 	}
-	return res
-}
-
-type entry struct {
-	sum, left, right int
-}
-
-func (e *entry) isOverlapping(other *entry) bool {
-	return max(e.left, other.left) <= min(e.right, other.right)
-}
-
-func sums(A []int, l int) []*entry {
-	n := len(A)
-	res := make([]*entry, n-l+1)
-	sum := 0
-	for i := 0; i < l; i++ {
-		sum += A[i]
+	// assume original A is A'
+	// now, A[i] = sum(A'[:i+1])
+	res, lMax, mMax := A[L+M-1], A[L-1], A[M-1]
+	for i := L + M; i < len(A); i++ {
+		// lMax is max sum of contiguous L elements before the last M elements.
+		lMax = max(lMax, A[i-M]-A[i-L-M])
+		// mMax is max sum of contiguous M elements before the last L elements.
+		mMax = max(mMax, A[i-L]-A[i-L-M])
+		res = max(res, max(lMax+A[i]-A[i-M], mMax+A[i]-A[i-L]))
 	}
-	for i := l; i < n; i++ {
-		res[i-l] = &entry{
-			sum:   sum,
-			left:  i - l,
-			right: i - 1,
-		}
-		sum += A[i] - A[i-l]
-	}
-	res[n-l] = &entry{
-		sum:   sum,
-		left:  n - l,
-		right: n - 1,
-	}
-	sort.Slice(res, func(i int, j int) bool {
-		return res[i].sum > res[j].sum
-	})
 	return res
 }
 
@@ -61,10 +25,3 @@ func max(a, b int) int {
 	}
 	return b
 }
-
-func min(a, b int) int {
-	if a < b {
-		return a
-	}
-	return b
-}

Algorithms/1031.maximum-sum-of-two-non-overlapping-subarrays/maximum-sum-of-two-non-overlapping-subarrays_test.go

@@ -1,7 +1,6 @@
 package problem1031
 
 import (
-	"reflect"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
@@ -68,36 +67,3 @@ func Benchmark_maxSumTwoNoOverlap(b *testing.B) {
 		}
 	}
 }
-
-func Test_sums(t *testing.T) {
-	type args struct {
-		A []int
-		l int
-	}
-	tests := []struct {
-		name string
-		args args
-		want []*entry
-	}{
-		{
-			"test",
-			args{
-				A: []int{0, 1, 2, 3},
-				l: 3,
-			},
-			[]*entry{
-				&entry{6, 1, 3},
-				&entry{3, 0, 2},
-			},
-		},
-
-		// TODO: Add test cases.
-	}
-	for _, tt := range tests {
-		t.Run(tt.name, func(t *testing.T) {
-			if got := sums(tt.args.A, tt.args.l); !reflect.DeepEqual(got, tt.want) {
-				t.Errorf("sums() = %v, want %v", got, tt.want)
-			}
-		})
-	}
-}