剑指offer打卡 week2

24. 机器人的运动范围

https://www.acwing.com/problem/content/22/

class Solution {
public:

    int get_sum(pair<int, int> p) {
        int s = 0;
        while (p.first) {
            s += p.first % 10;
            p.first /= 10;
        }
        while (p.second) {
            s += p.second % 10;
            p.second /= 10;
        }
        return s;
    }

    int movingCount(int threshold, int rows, int cols)
    {
        if (!rows || !cols) return 0;
        queue<pair<int,int>> q;
        vector<vector<bool>> st(rows, vector<bool>(cols, false));

        int dx[4] = {-1, 0, 1, 0}, dy[4] = {0, 1, 0, -1};

        int res = 0;
        q.push({0, 0});
        while (q.size()) {
            auto t = q.front();
            q.pop();
            if (st[t.first][t.second] || get_sum(t) > threshold) continue;
            res ++ ;
            st[t.first][t.second] = true;
            for (int i = 0; i < 4; i ++ ) {
                int x = t.first + dx[i], y = t.second + dy[i];
                if (x >= 0 && x < rows && y >= 0 && y < cols) q.push({x, y});
            }
        }

        return res;
    }
};

25. 剪绳子

https://www.acwing.com/problem/content/24/

class Solution {
public:
    int maxProductAfterCutting(int n) {
        if(n<=3) return 1*(n-1);
        long long res=1;
        if(n%3==1){
            res=4;
            n-=4;
        }
        else if(n%3==2){
            res=2;
            n-=2;
        }
        while(n){
            n-=3;
            res*=3;
        }
        return res;
    }
};

26. 二进制中1的个数

https://www.acwing.com/problem/content/25/

class Solution {
public:
    int fun(int n){
        int x=0;
        long long temp=1;
        while(n){
            if(temp>n){
                n-=temp/2;
                temp=1;
                x++;
            }
            temp*=2;
        }
        return x;
    }
    int NumberOf1(int n) {
        int ans=0;
        if(n==0) return 0;
        else if(n>0) ans=fun(n);
        else ans=32-fun(n*-1-1);
        return ans;
    }
};

27. 数值的整数次方

https://www.acwing.com/problem/content/26/

class Solution {
public:
    double Power(double x, int n) {
        typedef long long LL;
        bool is_minus = n < 0;
        double res = 1;
        for (LL k = abs(LL(n)); k; k >>= 1) {
            if (k & 1) res *= x;
            x *= x;
        }
        if (is_minus) res = 1 / res;
        return res;
    }
};

28. 在O(1)时间删除链表结点

https://www.acwing.com/problem/content/85/
思路:
由于找不到前继节点,可以换个思路 复制下一个的值然后删除下一个节点达到目的

class Solution {
public:
    void deleteNode(ListNode* node) {
        auto nextptr=node->next;
        node->val=nextptr->val;
        node->next=nextptr->next;
        delete nextptr;
    }
};

29. 删除链表中重复的节点

https://www.acwing.com/problem/content/27/

class Solution {
public:
    ListNode* deleteDuplication(ListNode* head) {
        auto headptr=new ListNode(-1);
        headptr->next=head;
        auto p=headptr;
        while(p->next){
            auto q=p->next;
            while(q && p->next->val==q->val) q=q->next;
            if(p->next->next==q) p=p->next;
            else p->next=q;
        }
        return headptr->next;
    }
};

32. 调整数组顺序使奇数位于偶数前面

https://www.acwing.com/problem/content/30/

class Solution {
public:
    void reOrderArray(vector<int> &array) {
        int l=0,r=array.size()-1;
        while(l<r){
            while(l<r && array[l]%2==1) l++;
            while(l<r && array[r]%2==0) r--;
            if(l<r){
                swap(array[l],array[r]);
            }
        }
    }
};

33. 链表中倒数第k个节点

https://www.acwing.com/problem/content/32/

class Solution {
public:
    ListNode* findKthToTail(ListNode* pListHead, int k) {
        if(pListHead==NULL) return NULL;
        auto head=pListHead;
        int len=1;
        while(pListHead->next){
            len++;
            pListHead=pListHead->next;
        }
        if(k>len) return NULL;
        len=len-k;
        pListHead=head;
        while(len--){
            pListHead=pListHead->next;
        }
        return pListHead;
    }
};

34. 链表中环的入口结点

https://www.acwing.com/problem/content/86/

class Solution {
public:
    ListNode *entryNodeOfLoop(ListNode *head) {
        if (!head || !head->next) return 0;
        auto first=head;
        auto second=head;
        while(first->next && first->next->next){
            first=first->next->next;
            second=second->next;
            if(first==second) {
                second=head;
                while(first!=second){
                    first=first->next;
                    second=second->next;
                }
                return second;
            }
        }
        return NULL;
    }
};