参考大佬代码：（区间合并+二分）

import os
import sys

n, L = map(int, input().split())  # 输入n,len
arr = [list(map(int, input().split())) for _ in range(n)]  # 输入Li,Si
def check(Ti, arr, L)->bool:
    sec = []  # 存入已打开的阀门在Ti时刻能检测到水流的管道区间
    for Li, Si in arr:  # 遍历已打开的阀门，计算存入能检测到水流的管道区间
        if Ti >= Si:
            sec.append((Li - (Ti-Si), Li + (Ti-Si)))

    sec.sort()
    if not sec or sec[0][0] > 1:
        return False
    rboundary = sec[0][1]  # 初始化最大右边界

    for i in range(1, len(sec)):  # 遍历管道区间并合并相邻区间
        if sec[i][0] - rboundary <= 1:
            rboundary = max(rboundary, sec[i][1])
        else:
            break
    return rboundary >= L

l,r = 0,10**9
while l < r:  # 二分
    mid = (l + r) // 2
    if check(mid, arr, L):
        r = mid
    else:
        l = mid + 1
print(l)