代码 1 动态规划：

动态转移方程

当然下面代码依然可以优化

1. up 结尾为上升
2. down 结尾为下降

func wiggleMaxLength(nums []int) int {
    n := len(nums)
    if n < 2 {
        return n
    }
    up := make([]int, n)
    down := make([]int, n)
    up[0] = 1
    down[0] = 1
    for i := 1; i < n; i++ {
        if nums[i] > nums[i-1] {
            up[i] = max(up[i-1], down[i-1]+1)
            down[i] = down[i-1]
        } else if nums[i] < nums[i-1] {
            up[i] = up[i-1]
            down[i] = max(up[i-1]+1, down[i-1])
        } else {
            up[i] = up[i-1]
            down[i] = down[i-1]
        }
    }
    return max(up[n-1], down[n-1])
}

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

代码 1 优化

func wiggleMaxLength(nums []int) int {
    n := len(nums)
    if n < 2 {
        return n
    }
    up, down := 1, 1
    for i := 1; i < n; i++ {
        if nums[i] > nums[i-1] {
            up = down + 1
        }else if nums[i] < nums[i-1] {
            down = up + 1
        }
    } 
    if up > down {
        return up
    }
    return down
}

代码 2 贪心：

1. prediff 上一个差异
2. diff 当前差异

func wiggleMaxLength(nums []int) int {
    n := len(nums)
    if n < 2 {
        return n
    }
    ans := 1
    prevDiff := nums[1] - nums[0]
    if prevDiff != 0 {
        ans = 2
    }
    for i := 2; i < n; i++ {
        diff := nums[i] - nums[i-1]
        if diff > 0 && prevDiff <= 0 || diff < 0 && prevDiff >= 0 {
            ans++
            prevDiff = diff
        }
    }
    return ans
}