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max_sum_submatrix.go
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/
max_sum_submatrix.go
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package _363_max_sum_of_rectangle_no_larger_than_k
import (
"math"
"sort"
)
func maxSumSubmatrix(matrix [][]int, k int) int {
m, n := len(matrix), len(matrix[0])
vals := make([]int, n)
prefixSums := make(sortedIntSet, n)
bestResult := math.MinInt32
for startRow := range matrix {
for i := range vals {
vals[i] = 0
}
for row := startRow; row < m; row++ {
for col, val := range matrix[row] {
vals[col] += val
}
currSum := 0
maxSum := vals[0]
for _, val := range vals {
currSum = max(currSum+val, val)
maxSum = max(maxSum, currSum)
}
if maxSum <= k {
bestResult = max(bestResult, maxSum)
continue
}
currSum = 0
prefixSums = prefixSums[:1]
prefixSums[0] = 0
for _, val := range vals {
currSum += val
partnerIdx := sort.SearchInts(prefixSums, currSum-k)
if partnerIdx != len(prefixSums) {
bestResult = max(bestResult, currSum-prefixSums[partnerIdx])
}
prefixSums.insert(currSum)
}
}
}
return bestResult
}
func max(a, b int) int {
if a > b {
return a
}
return b
}
type sortedIntSet []int
func (s *sortedIntSet) insert(x int) {
i := sort.SearchInts(*s, x)
if i == len(*s) {
*s = append(*s, x)
} else if (*s)[i] != x {
*s = append(*s, 0)
copy((*s)[i+1:], (*s)[i:])
(*s)[i] = x
}
}