91）粉刷房子

二维dp

class Solution{
public:
    int minCost(vector<vector<int>>& costs){
        int n = costs.size();
        vector<vector<int>> f(n+1, vector<int>(costs[0].size(), 0));
        for(int i=1; i<=n; i++){
            for(int j=0; j<costs[0].size(); j++){
                f[i][j] = min(f[i-1][(j+1)%3], f[i-1][(j+2)%3]) + costs[i-1][j];
            }
        }
        int res = INT_MAX;
        for(int j=0; j<3; j++){
            res = min(res, f[n][j]);
        }
        return res;
    }
};

dp优化空间

class Solution{
public:
    int minCost(vector<vector<int>>& costs){
        int n = costs.size();
        int a0 = costs[0][0];
        int a1 = costs[0][1];
        int a2 = costs[0][2];
        for(int i=1; i<n; i++){
            int b0 = min(a1, a2)+costs[i][0];
            int b1 = min(a0, a2)+costs[i][1];
            int b2 = min(a0, a1)+costs[i][2];
            a0 = b0;
            a1 = b1;
            a2 = b2;
        }
        return min(a0, min(a1, a2));
    }
};

92)翻转字符

class Solution{
public:
    int minFlipsMonoIncr(string s){
        int n = s.size();
        vector<int> cnt(n+1, 0);
        for(int i=1; i<=n; i++){
            cnt[i] = cnt[i-1]+(s[i-1]=='1');
        }
        int res = INT_MAX;
        for(int i=0; i<=n; i++){
            res = min(res, cnt[i]+(n-i-cnt[n]+cnt[i]));
        }
        return res;
    }
};

93)最长斐波那契数列

class Solution{
public:
    int lenLongestFibSubseq(vector<int>& arr){
        vector<vector<int>> dp(arr.size(), vector<int>(arr.size()));
        unordered_map<int, int> mp;
        for(int i=0; i<arr.size(); i++){
            mp[arr[i]] = i;
        }
        int ret = 0;
        for(int i=1; i<arr.size(); i++){
            for(int j=0; j<i; j++){
                int temp = arr[i] - arr[j];
                if(mp.count(temp) && mp[temp]<j){
                    dp[i][j] = dp[j][mp[temp]]+1;
                }else{
                    dp[i][j] = 2;
                }
                ret = max(ret, dp[i][j]);
            }
        }
        return ret>2 ? ret : 0;
    }
};