题目：
题解：
Go
import "math/rand"
type node struct {
ch [2]*node
priority int
val int
}
func (o *node) cmp(b int) int {
switch {
case b < o.val:
return 0
case b > o.val:
return 1
default:
return -1
}
}
func (o *node) rotate(d int) *node {
x := o.ch[d^1]
o.ch[d^1] = x.ch[d]
x.ch[d] = o
return x
}
type treap struct {
root *node
}
func (t *treap) _put(o *node, val int) *node {
if o == nil {
return &node{priority: rand.Int(), val: val}
}
if d := o.cmp(val); d >= 0 {
o.ch[d] = t._put(o.ch[d], val)
if o.ch[d].priority > o.priority {
o = o.rotate(d ^ 1)
}
}
return o
}
func (t *treap) put(val int) {
t.root = t._put(t.root, val)
}
func (t *treap) lowerBound(val int) (lb *node) {
for o := t.root; o != nil; {
switch c := o.cmp(val); {
case c == 0:
lb = o
o = o.ch[0]
case c > 0:
o = o.ch[1]
default:
return o
}
}
return
}
func maxSumSubmatrix(matrix [][]int, k int) int {
ans := math.MinInt64
for i := range matrix { // 枚举上边界
sum := make([]int, len(matrix[0]))
for _, row := range matrix[i:] { // 枚举下边界
for c, v := range row {
sum[c] += v // 更新每列的元素和
}
t := &treap{}
t.put(0)
s := 0
for _, v := range sum {
s += v
if lb := t.lowerBound(s - k); lb != nil {
ans = max(ans, s-lb.val)
}
t.put(s)
}
}
}
return ans
}
func max(a, b int) int {
if a > b {
return a
}
return b
}