leetcode 42 接雨水
本题用双指针法更为浅显易懂
双指针法：
class Solution:
def trap(self, height: List[int]) -> int:
leftheight, rightheight = [0] * len(height), [0] * len(height)
ans = 0
leftheight[0] = height[0]
for i in range(1, len(height)):
leftheight[i] = max(height[i], leftheight[i - 1])
rightheight[-1] = height[-1]
for i in range(len(height) - 2, -1, -1):
rightheight[i] = max(height[i], rightheight[i + 1])
for i in range(len(height)):
total = min(leftheight[i], rightheight[i]) - height[i]
ans += total
return ans单调栈：
class Solution:
def trap(self, height: List[int]) -> int:
stack = [0]
ans = 0
for i in range(1, len(height)):
if height[i] < height[stack[-1]]:
stack.append(i)
elif height[i] == height[stack[-1]]:
stack.pop()
stack.append(i)
else:
while stack and height[i] > height[stack[-1]]:
mid_height = height[stack[-1]]
stack.pop()
if stack:
right_height = height[i]
left_height = height[stack[-1]]
h = min(right_height, left_height) - mid_height
w = i - stack[-1] - 1
ans += h * w
stack.append(i)
return ansleetcode 84 柱状图的最大的矩形
class Solution:
def largestRectangleArea(self, heights: List[int]) -> int:
heights.insert(0, 0)
heights.append(0)
stack = [0]
ans = 0
for i in range(1, len(heights)):
while stack and heights[i] < heights[stack[-1]]:
mid_height = heights[stack[-1]]
stack.pop()
if stack:
area = (i - stack[-1] - 1) * mid_height
ans = max(area, ans)
stack.append(i)
return ans双指针法：
class Solution:
def largestRectangleArea(self, heights: List[int]) -> int:
n = len(heights)
min_left_index = [0] * n
min_right_index = [0] * n
min_left_index[0] = -1
result = 0
for i in range(1, n):
temp = i - 1
while temp >= 0 and heights[temp] >= heights[i]:
temp = min_left_index[temp]
min_left_index[i] = temp
min_right_index[n - 1] = n
for i in range(n - 2, -1, -1):
temp = i + 1
while temp < n and heights[temp] >= heights[i]:
temp = min_right_index[temp]
min_right_index[i] = temp
for i in range(len(heights)):
area = heights[i] * (min_right_index[i] - min_left_index[i] -1)
result = max(result, area)
return result
