[刷力扣] 61-70题

文章目录

• 61. 旋转链表
• 62. 不同路径
• 63. 不同路径 II
• 64. 最小路径和
• 65. 有效数字
• 66. 加一
• 67. 二进制求和
• 68. 文本左右对齐
• 69. x 的平方根
• 70. 爬楼梯

61. 旋转链表

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode() : val(0), next(nullptr) {}
 *     ListNode(int x) : val(x), next(nullptr) {}
 *     ListNode(int x, ListNode *next) : val(x), next(next) {}
 * };
 */
class Solution {
public:
    ListNode* rotateRight(ListNode* head, int k) {
        if (!head) return head;
        ListNode *now = head, *last = head, *pre = head;
        int len = 0;
        while (now) len ++, last = now, now = now->next;
        k %= len;
        k = len - k;
        if (!k || k == len) return head;
        now = head;
        while (k --) pre = now, now = now->next;
        last->next = head;
        pre->next = nullptr;
        return now;
    }
};

62. 不同路径

class Solution {
public:
    int uniquePaths(int m, int n) {
        vector<vector<int>> f(m, vector<int>(n, 0));
        for (int i = 0; i < m; ++ i) f[i][0] = 1;
        for (int i = 0; i < n; ++ i) f[0][i] = 1;
        for (int i = 1; i < m; ++ i)
        for (int j = 1; j < n; ++ j)
            f[i][j] += f[i - 1][j] + f[i][j - 1];
        return f[m - 1][n - 1];
    }
};

63. 不同路径 II

class Solution {
public:
    int uniquePathsWithObstacles(vector<vector<int>>& o) {
        int n = o.size(), m = o.back().size();
        vector<vector<int>> f(n, vector<int>(m, 0));
        for (int i = 0; i < n && (o[i][0] == 0); ++ i) f[i][0] = 1;
        for (int i = 0; i < m && (o[0][i] == 0); ++ i) f[0][i] = 1;
        for (int i = 1; i < n; ++ i)
        for (int j = 1; j < m; ++ j) {
            if (o[i][j]) continue;
            if (!o[i - 1][j]) f[i][j] += f[i - 1][j];
            if (!o[i][j - 1]) f[i][j] += f[i][j - 1];
        }
        return f[n - 1][m - 1];
    }
};

64. 最小路径和

class Solution {
public:
    int minPathSum(vector<vector<int>>& grid) {
        int n = grid.size(), m = grid.back().size();
        vector<vector<int>> f(n, vector<int>(m, 0));
        f[0][0] = grid[0][0];
        for (int i = 1; i < n; ++ i) f[i][0] = f[i - 1][0] + grid[i][0];
        for (int i = 1; i < m; ++ i) f[0][i] = f[0][i - 1] + grid[0][i];
        for (int i = 1; i < n; ++ i)
        for (int j = 1; j < m; ++ j)
            f[i][j] = min(f[i - 1][j], f[i][j - 1]) + grid[i][j];
        return f[n - 1][m - 1];
    }
};

65. 有效数字

class Solution {
public:
    bool isNumber(string s) {
        auto isInt = [=](string s) -> bool {
            int st = 0;
            if (s[st] == '+' || s[st] == '-') st ++;
            for (; st < s.size(); ++ st) 
                if (s[st] < '0' || s[st] > '9') return false;
            return true;
        };
        auto check = [](string b) -> bool{
            if (b.size() != 1) return true;
            if (b.back() == '+' || b.back() == '-') return false;
            return true;
        };
        auto isFol = [=](string s) -> bool {
            int st = s.find('.');
            if (st == s.npos) return false;
            if (s.size() == 1) return false;
            string a = s.substr(0, st);
            if (st && !isInt(a)) return false;
            if (st + 1 != s.size()) {
                string tmp = s.substr(st + 1);
                tmp = "+" + tmp;
                return isInt(tmp);
            }
            int flag = 0;
            for (int i = 0; i < s.size(); ++ i)
                flag += (s[i] >= '0' && s[i] <= '9');
            return flag != 0;
        };
        
        transform(s.begin(),s.end(),s.begin(),::tolower);
        int st = s.find('e');
        if (st == s.npos) return isInt(s) || isFol(s);
        else {
            if (st == 0 || st == s.size() - 1) return false;
            string a = s.substr(0, st);
            string b = s.substr(st + 1);
            return (isFol(a) || isInt(a)) && isInt(b) && check(b) && check(a);
        }
    }
};

66. 加一

class Solution {
public:
    vector<int> plusOne(vector<int>& digits) {
        reverse(digits.begin(), digits.end());
        int t = 1;
        for (int i = 0; i < digits.size(); ++ i) {
            t += digits[i];
            digits[i] = t % 10;
            t /= 10;
        }
        if (t) digits.push_back(t);
        reverse(digits.begin(), digits.end());
        return digits;
    }
};

67. 二进制求和

class Solution {
public:
    string addBinary(string a, string b) {
        string ans;
        reverse(begin(a), end(a));
        reverse(begin(b), end(b));
        int t = 0;
        for (int i = 0; i < max(a.size(), b.size()); ++ i) {
            if (i < a.size()) t += (a[i] == '1');
            if (i < b.size()) t += (b[i] == '1');
            ans.push_back((t % 2) + '0');
            t /= 2;
        }
        if (t) ans.push_back('1');
        reverse(begin(ans), end(ans));
        return ans;
    }
};

68. 文本左右对齐

class Solution {
public:
    vector<string> fullJustify(vector<string>& words, int maxWidth) {
        vector<string> ans;
        vector<string> temp;
        int cur = 0;
        for (int i = 0; i < words.size(); ++ i) {
            
            if (maxWidth >= cur + temp.size() + words[i].size()) {
                temp.push_back(words[i]);
                cur += words[i].size();
            } else {
                string s;
                if (temp.size() > 1) {
                    int space = maxWidth - (cur + temp.size() - 1);
                    int siz   = space / (temp.size() - 1);
                    int to    = space % (temp.size() - 1);
                    for (int i = 0; i < temp.size(); ++ i) {
                        if (i) {
                            s = s + string(1 + siz + (!!to),' ') + temp[i];
                            if (to) to --;
                        } else s = temp[i];
                    }
                } else s = temp[0];
                if (s.size() < maxWidth) s += string(maxWidth - s.size(), ' ');
                ans.push_back(s);
                vector<string>().swap(temp);
                temp.push_back(words[i]);
                cur = words[i].size();
            }
        }
        string s;
        for (int i = 0; i < temp.size(); ++ i) 
            if (i) s += " " + temp[i];
            else s += temp[i];
        if (s.size() < maxWidth) s += string(maxWidth - s.size(), ' ');
        ans.push_back(s);
        return ans;
    }
};

69. x 的平方根

class Solution {
public:
    int mySqrt(int x) {
        long long l = 0, r = x;
        while (l < r) {
            long long mid = l + r + 1>> 1;
            if (mid * mid <= x) l = mid;
            else r = mid - 1;
        }
        return l;
    }
};

70. 爬楼梯

class Solution {
public:
    int climbStairs(int n) {
        vector f(n + 1, 0);
        f[0] = 1;f[1] = 1;
        for (int i = 2; i <= n; ++ i) f[i] = f[i - 1]  + f[i - 2];
        return f[n];
    }
};