题目：

题解：

func findMaxLength(nums []int) (maxLength int) {
    mp := map[int]int{0: -1}
    counter := 0
    for i, num := range nums {
        if num == 1 {
            counter++
        } else {
            counter--
        }
        if prevIndex, has := mp[counter]; has {
            maxLength = max(maxLength, i-prevIndex)
        } else {
            mp[counter] = i
        }
    }
    return
}

func max(a, b int) int {
    if a > b {
        return a
    }
    return b
}