LeetCode 209. 长度最小的子数组
子数组是一个连续的，很容易想到滑动窗口
class Solution:def minSubArrayLen(self, target: int, nums: List[int]) -> int:windowSum = 0left, right = 0, 0res = float('inf')while right < len(nums):push = nums[right]windowSum += pushright += 1while windowSum >= target:res = min(res, right - left)pop = nums[left]windowSum -= popleft += 1return res if res != float('inf') else 0
拓展
如果 nums 数组中包含负数，则窗口扩大时元素和不见得就增大，窗口缩小时元素和不见得就减小，这种情况就不能单纯使用滑动窗口技巧了，可能需要混合动态规划和单调队列来做。
862. 和至少为 K 的最短子数组
LeetCode 1425. 带限制的子序列和
LeetCode 53. 最大子数组和
这里给出的是滑动窗口解法
class Solution:def maxSubArray(self, nums: List[int]) -> int:windowSum = 0res = float("-inf")left = right = 0while right < len(nums):push = nums[right]windowSum += pushright += 1res = max(res, windowSum)while windowSum < 0:pop = nums[left]windowSum -= popleft += 1return res
LeetCode 59. 螺旋矩阵 II
模拟题，做这一题之前可以先试试 LeetCode 54. 螺旋矩阵
class Solution:def generateMatrix(self, n: int) -> List[List[int]]:matrix = [[None for _ in range(n)] for _ in range(n)]idx = 1a, b, x, y = 0, 0, n - 1, n - 1for _ in range(n ** 2):for j in range(b, y + 1):matrix[a][j] = idxidx += 1a += 1for i in range(a, x + 1):matrix[i][y] = idxidx += 1y -= 1for j in range(y, b - 1, -1):matrix[x][j] = idxidx += 1x -= 1for i in range(x, a - 1, -1):matrix[i][b] = idxidx += 1b += 1return matrix
LeetCode 54. 螺旋矩阵
class Solution:def spiralOrder(self, matrix: List[List[int]]) -> List[int]:m, n = len(matrix) - 1, len(matrix[0]) - 1x, y = 0, 0res = []while x <= m and y <= n:for j in range(y, n + 1):if x <= m and y <= n:res.append(matrix[x][j])x += 1for i in range(x, m + 1):if x <= m and y <= n:res.append(matrix[i][n])n -= 1for j in range(n, y - 1, -1):if x <= m and y <= n:res.append(matrix[m][j])m -= 1for i in range(m, x - 1, -1):if x <= m and y <= n:res.append(matrix[i][y])y += 1return res
KamaCoder 44. 开发商购买土地
前缀和思想
import sysdef find(matrix):m, n = len(matrix), len(matrix[0])preSum_matrix = [[None for _ in range(n)] for _ in range(m)]preSum_matrix[0][0] = matrix[0][0]for i in range(m):for j in range(n):up = preSum_matrix[i - 1][j] if i - 1 >= 0 else 0left = preSum_matrix[i][j - 1] if j - 1 >= 0 else 0left_up = preSum_matrix[i - 1][j - 1] if i - 1 >= 0 and j - 1 >= 0 else 0preSum_matrix[i][j] = matrix[i][j] + up + left - left_upres = float('inf')for i in range(m - 1):if res == 0:return 0res = min(res, abs(preSum_matrix[m - 1][n - 1] - preSum_matrix[i][n - 1] * 2))for j in range(n - 1):if res == 0:return 0res = min(res, abs(preSum_matrix[m - 1][n - 1] - preSum_matrix[m - 1][j] * 2))return resif __name__ == "__main__":lines = sys.stdin.read().strip().splitlines()idx = 0res = []while idx < len(lines):m, n = map(int, lines[idx].strip().split())idx += 1matrix = []for _ in range(m):line = list(map(int, lines[idx].strip().split()))matrix.append(line)idx += 1res.append(str(find(matrix)))sys.stdout.write("\n".join(res))
