题目链接:https://leetcode.com/problems/house-robber/
答案自然是动态规划(Dynamic programming,简称DP)。
代码
func rob1(nums []int) int {
lth := len(nums)
if lth == 0 {
return 0
}
dp := make([]int, lth+1)
dp[1] = nums[0]
for i := 2; i < lth+1; i++ {
dp[i] = int(math.Max(float64(nums[i-1] + dp[i-2]), float64(dp[i-1])))
}
return dp[lth]
}
变种题House Robber II
代码
func rob2(nums []int) int {
lth := len(nums)
if lth == 0 {
return 0
} else if lth == 1 {
return nums[0]
}
return int(math.Max(float64(rob1(nums[:lth-1])), float64(rob1(nums[1:lth]))))
}
第一次做的时候,我并不是这么写的。
受到《算法导论》中矩阵链乘法的影响,我采用的是二维视角。
rob1的代码如下:
func rob1(nums []int) int {
lth := len(nums)
if lth == 0 {
return 0
} else if lth == 1 {
return nums[0]
} else if lth == 2 {
return int(math.Max(float64(nums[0]), float64(nums[1])))
}
dp := make([][]int,lth+1)
for i := 0; i <= lth; i++ {
dp[i] = make([]int,lth+1)
}
// 长度为1的
for i := 1; i <= lth; i++ {
dp[i][i] = nums[i-1]
}
// 长度为2的
for i := 1; i < lth; i++ {
dp[i][i+1] = int(math.Max(float64(nums[i-1]),float64(nums[i])))
}
// 长度>=3的
for l := 3; l <= lth;l++ {
for i := 1; i <= lth+1 - l; i++ {
j := i+ l -1
dp[i][j] = int(math.Max(float64(dp[i][j-1]), float64(dp[i][j-2] + nums[j-1])))
}
}
return dp[1][lth]
}
rob2相比rob1,只有在长度为n的情况下,才需要特殊处理下
func rob2(nums []int) int {
lth := len(nums)
if lth == 0 {
return 0
} else if lth == 1 {
return nums[0]
} else if lth == 2 {
return int(math.Max(float64(nums[0]), float64(nums[1])))
}
dp := make([][]int,lth+1)
for i := 0; i <= lth; i++ {
dp[i] = make([]int,lth+1)
}
// 长度为1的
for i := 1; i <= lth; i++ {
dp[i][i] = nums[i-1]
}
// 长度为2的
for i := 1; i < lth; i++ {
dp[i][i+1] = int(math.Max(float64(nums[i-1]),float64(nums[i])))
}
// 长度>=3的
for l := 3; l < lth;l++ {
for i := 1; i <= lth+1 - l; i++ {
j := i+ l -1
dp[i][j] = int(math.Max(float64(dp[i][j-1]), float64(dp[i][j-2] + nums[j-1])))
}
}
return int(math.Max(float64(dp[1][lth-1]),float64(dp[2][lth-2] + nums[lth-1])))
}