题目

house-robber/

算法

* DP

* DP优化

代码

* DP

// DP
/ DP
class Solution {
public:
    int rob(vector<int>& nums) {
        if (nums.size() <= 1) return nums.empty() ? 0 : nums[0];
        return max(rob(nums, 0, nums.size() - 1), rob(nums, 1, nums.size()));
    }
    int rob(vector<int> &nums, int left, int right) {
        if (right - left <= 1) return nums[left];
        vector<int> dp(right, 0);
        dp[left] = nums[left];
        dp[left + 1] = max(nums[left], nums[left + 1]);
        for (int i = left + 2; i < right; ++i) {
            dp[i] = max(nums[i] + dp[i - 2], dp[i - 1]);
        }
        return dp.back();
    }
};

* DP优化

class Solution {
public:
    int rob(vector<int>& nums) {
        if (nums.size() <= 1) return nums.empty() ? 0 : nums[0];
        return max(rob(nums, 0, nums.size() - 1), rob(nums, 1, nums.size()));
    }
    int rob(vector<int> &nums, int left, int right) {
        int a = 0, b = 0;
        for (int i = left; i < right; ++i) {
            int m = a, n = b;
            a = n + nums[i];
            b = max(m, n);
        }
        return max(a, b);
    }
};

* 更优化

class Solution {
public:
    int rob(vector<int>& nums) {
        if (nums.size() <= 1) return nums.empty() ? 0 : nums[0];
        vector<int> v1 = nums, v2 = nums;
        v1.erase(v1.begin()); v2.pop_back();
        return max(rob_house(v1), rob_house(v2));
    }
    int rob_house(vector<int> &nums) {
        int a = 0, b = 0;
        for (int i = 0; i < nums.size(); ++i) {
            if (i % 2 == 0) {
                a += nums[i];
                a = max(a, b);
            } else {
                b += nums[i];
                b = max(a, b);
            }
        }
        return max(a, b);
    }
};