【入门夯实】双指针技巧：有序数据的对撞搜索写法

for i = 1, #arr do
    for j = 1, #arr do
        if arr[i] + arr[j] == target then
            return i, j
        end
    end
end

local function twoSum(arr, target)
    local left, right = 1, #arr
    while left < right do
        local sum = arr[left] + arr[right]
        if sum == target then
            return left, right
        end
        if sum < target then
            left = left + 1
        else
            right = right - 1
        end
    end
    return nil
end

local function hasCycle(links, start)
    local slow, fast = start, start
    while true do
        slow = links[slow]
        fast = links[links[fast]]
        if slow == nil or fast == nil then
            return false
        end
        if slow == fast then
            return true
        end
    end
end