Weekly Contest 95
程序员文章站
2022-07-15 11:13:26
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/**
* Definition for singly-linked list.
* struct ListNode {
* int val;
* ListNode *next;
* ListNode(int x) : val(x), next(NULL) {}
* };
*/
class Solution {
public:
int get_nodes(ListNode* head){
ListNode* p = head;
int node_num = 0;
while(p){
node_num ++;
p = p->next; //not p ++(用于数组指针)
}
return node_num;
}
ListNode* middleNode(ListNode* head) {
ListNode* mid_node = head;
int step = get_nodes(head)/2;
for(int i=1;i<=step;i++) mid_node = mid_node->next;
return mid_node;
}
};
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2 . 877. 石子游戏
class Solution {
public:
//dp[i][j]: 区间长度为i且下标从j开始时先手多出的石子数
bool stoneGame(vector<int>& piles) {
int len = piles.size();
vector<vector <int>> dp = vector<vector <int>> (len + 5, vector<int>(len + 5)); //创建二维数组
for(int i=0;i<len;i++) dp[1][i] = piles[i];
for(int i=2;i<=len;i++){
for(int j=0;j+i<=len;j++){
dp[i][j] = max(piles[j] - dp[i-1][j+1], piles[j+i-1] - dp[i-1][j]);
}
}
return dp[len][0] > 0;
}
};
3 . 878. 第 N 个神奇数字
const int P = 1e9 + 7;
typedef long long ll;
class Solution {
public:
int gcd(int A, int B){
int rem = A % B;
while(rem) {
A = B;
B = rem;
rem = A % B;
}
return B;
}
int nthMagicalNumber(int N, int A, int B) {
ll low = 1, high = min(A, B)*(ll)N; //
int lcm = A * B / gcd(A, B);
while(low < high){
ll mid = (low + high) >> 1;
//'>''='放一起是因为可能在mid不整除A或B的情况下计算结果为N,譬如A = 2, B = 3, N = 4, 此时mid = 6 或 7
if(mid/A + mid/B - mid/lcm >= N) high = mid;
else low = mid + 1;
}
return low % P;
}
};
4 . 879. 盈利计划
const int PR = 1e9 + 7;
class Solution {
public:
//dp[i][j]:i名成员的犯罪计划至少产生利润j的方案数
int profitableSchemes(int G, int P, vector<int>& group, vector<int>& profit) {
vector<vector <int >> dp(G + 5, vector<int>(P + 5)); //默认为0
dp[0][0] = 1;
//背包
for(int k = 0; k < group.size(); k++) {
//这两个循环都是从大到小(两者顺序不受限制)
for(int j = P; j >= 0; j--) {
for(int i = G-group[k]; i >= 0; i--) {
//for(int j = P; j >= 0; j--) {
if(dp[i][j]) (dp[i+group[k]][min(P, j+profit[k])] += dp[i][j]) %= PR; //
}
}
}
int ret = 0;
for(int i = 0; i <= G; i++) (ret += dp[i][P]) %= PR; //%=
return ret;
}
};
参照:
【1】: [email protected]阳谷县
【2】: wangyisong-CN