2020-03-01：给定一个非负数组arr，代表直方图。返回直方图的最大长方形面积。
福哥答案2020-03-01：
单调栈，大压小。有代码。
代码用golang编写，代码如下：
package main
import (
"container/list"
"fmt"
)
func main() {
arr := []int{3, 2, 4, 2, 5}
fmt.Println(largestRectangleArea1(arr))
fmt.Println(largestRectangleArea2(arr))
}
func largestRectangleArea1(height []int) int {
if len(height) == 0 {
return 0
}
maxArea := 0
stack := list.New().Init()
N := len(height)
for i := 0; i < N; i++ {
for !(stack.Len() == 0) && height[i] <= height[stack.Back().Value.(int)] {
j := stack.Back().Value.(int)
stack.Remove(stack.Back())
k := 0
if stack.Len() == 0 {
k = -1
} else {
k = stack.Back().Value.(int)
}
curArea := (i - k - 1) * height[j]
maxArea = getMax(maxArea, curArea)
}
stack.PushBack(i)
}
for !(stack.Len() == 0) {
j := stack.Back().Value.(int)
stack.Remove(stack.Back())
k := 0
if stack.Len() == 0 {
k = -1
} else {
k = stack.Back().Value.(int)
}
curArea := (N - k - 1) * height[j]
maxArea = getMax(maxArea, curArea)
}
return maxArea
}
func largestRectangleArea2(height []int) int {
if len(height) == 0 {
return 0
}
N := len(height)
stack := make([]int, N)
si := -1
maxArea := 0
for i := 0; i < N; i++ {
for si != -1 && height[i] <= height[stack[si]] {
j := stack[si]
si--
k := 0
if si == -1 {
k = -1
} else {
k = stack[si]
}
curArea := (i - k - 1) * height[j]
maxArea = getMax(maxArea, curArea)
}
si++
stack[si] = i
}
for si != -1 {
j := stack[si]
si--
k := 0
if si == -1 {
k = -1
} else {
k = stack[si]
}
curArea := (N - k - 1) * height[j]
maxArea = getMax(maxArea, curArea)
}
return maxArea
}
func getMax(a int, b int) int {
if a > b {
return a
} else {
return b
}
}执行结果如下：