记录写hot100的代码（持续更新中...）

joseri

已于 2025-02-12 00:28:05 修改

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文章标签：算法哈希算法 leetcode

于 2025-02-07 21:12:27 首次发布

本文链接：https://blog.youkuaiyun.com/qq_45579784/article/details/145502711

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哈希 3 题

1 两数之和

class Solution {
public:
    vector<int> twoSum(vector<int>& nums, int target) {
        int n = nums.size();
        unordered_map<int, int> mp;
        for(int i = 0; i < n; i ++ ) {
            if(mp[target - nums[i]]) 
                return {i, mp[target - nums[i]] - 1};
            mp[nums[i]] = i + 1;
        }
        return {};
    }
};

49 字母异位词分组

Cpp

class Solution {
public:
    vector<vector<string>> groupAnagrams(vector<string>& strs) {
        vector<vector<string>> ans;
        int n = strs.size();
        unordered_map<string, vector<string>> mp;
        for(auto str: strs) {
            string ss = str;
            sort(ss.begin(), ss.end());
            mp[ss].push_back(str);
        }
        for(auto [k, v]: mp) {
            ans.push_back(v);
        }
        return ans;
    }
};

128 最长连续序列

Cpp

class Solution {
public:
    int longestConsecutive(vector<int>& nums) {
        int n = nums.size();
        unordered_set<int> st(nums.begin(), nums.end());
        int ans = 0;

        for(auto num : st) {
            if(st.count(num - 1) == 0) {
                int l = num, r = num + 1;
                while(st.find(r) != st.end()) r ++;
                ans = max(ans, r - l);
            }
        }
        return ans;
    }
};

双指针 4 题

283 移动零

class Solution {
public:
    void moveZeroes(vector<int>& nums) {
        int n = nums.size();
        int l = 0, r = 0;
        while(r < n) {
            if(nums[r]) {
                swap(nums[l], nums[r]);
                l ++;
            }
            r ++;
        }
    }
};

11 承最多水的容器

class Solution {
public:
    int maxArea(vector<int>& h) {
        int n = h.size();
        int l = 0, r = n - 1;
        int ans = 0;
        while(l < r) {
            if(l < r && h[l] < h[r]) {
                ans = max(ans, h[l] * (r - l));
                l ++;
            } else if(l < r && h[l] >= h[r]) {
                ans = max(ans, h[r] * (r - l));
                r --;
            }
        }
        return ans;
    }
};

15 三数之和

class Solution {
public:
    vector<vector<int>> threeSum(vector<int>& nums) {
        sort(nums.begin(), nums.end());
        unordered_map<int, int> mp;
        vector<vector<int>> ans;
        int n = nums.size();
        for(int i = 0; i < n; i ++ ) mp[nums[i]] = i;

        for(int i = 0; i < n; ) {
            for(int j = i + 1; j < n; ) {
                int x = nums[i], y = nums[j], z = -nums[i] - nums[j];
                if(mp[z] > j) {
                    ans.push_back({x, y, z});
                }
                int p = j;
                while(p < n && nums[p] == nums[j]) p ++;
                j = p;
            }
            int q = i;
            while(q < n && nums[q] == nums[i]) q ++;
            i = q;
        }
        return ans;
    }
};

42 接雨水

class Solution {
public:
    int trap(vector<int>& h) {
        int n = h.size();
        vector<int> l(n), r(n);
        l[0] = h[0];
        for(int i = 1; i < n; i ++ ) l[i] = max(l[i - 1], h[i]);
        r[n - 1] = h[n - 1];
        for(int i = n - 2; i >= 0; i -- ) r[i] = max(r[i + 1], h[i]);

        int ans = 0;
        for(int i = 0; i < n; i ++ ) 
            ans += min(l[i], r[i]) - h[i];
        return ans;
    }
};

滑动窗口 2 题

3 无重复字符的最长字串

class Solution {
public:
    int lengthOfLongestSubstring(string s) {
        int n = s.size();
        int l = 0, r = 0;
        int ans = 0;
        unordered_map<char, int> cnt;
        while(r < n) {
            cnt[s[r]] ++;
            while(l < n && cnt[s[r]] >= 2) {
                cnt[s[l]] --;
                l ++;
            }
            ans = max(ans, r - l + 1);
            r ++;
        }
        return ans;
    }
};

438 找到字符串中所有字母异位词

class Solution {
public:
    bool vec_eq(vector<int> a, vector<int> b) {
        int n = a.size();
        for(int i = 0; i < 26; i ++ ) 
            if(a[i] != b[i]) return false;
        return true;
    }
    vector<int> findAnagrams(string s, string p) {
        int n = s.size(), m = p.size();
        vector<int> cnts(26), cntp(26), ans;
        for(auto x : p) 
            cntp[x - 'a'] ++;

        int l = 0, r = 0;
        while(r < n) {
            cnts[s[r] - 'a'] ++;
            if(r - l + 1 == m) {
                if(vec_eq(cnts, cntp)) ans.push_back(l);
                cnts[s[l] - 'a'] --;
                l ++;
            }
            r ++;
        }

        return ans;
    }
};

字串 3 题

560 和为 k 的子数组

class Solution {
public:
    int subarraySum(vector<int>& nums, int k) {
        int n = nums.size();
        vector<int> sum(n + 1, 0);
        for(int i = 0; i < n; i ++ ) {
            sum[i + 1] = sum[i] + nums[i];
        }
        int ans = 0;
        unordered_map<int, int> mp;
        for(int i = 0; i <= n; i ++ ) {
            ans += mp[sum[i] - k];
            mp[sum[i]] ++;
        }
        return ans;
    }
};

239 滑动窗口最大值

class Solution {
public:
    vector<int> maxSlidingWindow(vector<int>& nums, int k) {
        int n = nums.size();
        priority_queue<pair<int, int>> pq;
        vector<int> ans;
        for(int i = 0; i < k; i ++ ) {
            pq.push({nums[i], i});
        }
        ans.push_back(pq.top().first);
        for(int i = k; i < n; i ++ ) {
            pq.push({nums[i], i});
            while(pq.top().second <= i - k) pq.pop();
            ans.push_back(pq.top().first);
        }
        return ans;
    }
};

76 最小覆盖字串

// TODO

class Solution {
public:
    string minWindow(string s, string t) {
        int n = s.size(), m = t.size();
        int l = 0, r = 0;
        vector<int> cnt(52, 0), cnt2(52, 0);
        for(auto ch: t) {
            if(ch >= 'A' && ch <= 'Z') cnt2[ch - 'A'] ++;
            else cnt2[ch - 'a' + 26] ++;
        }
        int ans = 1e6;
        int x = -1, y = -1;
        while(r < n) {
            if(s[r] >= 'A' && s[r] <= 'Z') cnt[s[r] - 'A'] ++;
            else cnt[s[r] - 'a' + 26] ++;
            // cnt[s[r]] ++;
            bool ok = true;
            for(int i = 0; i < 52; i ++ ) {
                if(cnt[i] < cnt2[i]) {ok = false; break;}
            }
            while(ok) {
                if(r - l + 1 <= ans) {
                    ans = r - l + 1;
                    x = l, y = r;
                }
                if(s[l] >= 'A' && s[l] <= 'Z') cnt[s[l] - 'A'] --;
                else cnt[s[l] - 'a' + 26] ++;
                // cnt[s[l]] --;
                l ++;
                for(int i = 0; i < 52; i ++ ) {
                    if(cnt[i] < cnt2[i]) {ok = false; break;}
                }                
            }
            r ++;
        }
        string ss = "";
        if(x == -1 || y == -1) return ss;
        else return s.substr(x, y - x + 1);
    }
};

普通数组 5 题

53 最大子数组和

class Solution {
public:
    int maxSubArray(vector<int>& nums) {
        int n = nums.size();
        vector<int> dp(n);
        dp[0] = nums[0];
        for(int i = 1; i < n; i ++ ) {
            dp[i] = max(dp[i - 1] + nums[i], nums[i]);
        }
        int ans = -2e9;
        for(int i = 0; i < n; i ++ ) {
            ans = max(ans, dp[i]);
        }
        return ans;
    }
};

56 合并数组

class Solution {
public:
    vector<vector<int>> merge(vector<vector<int>>& intervals) {
        vector<vector<int>> ans;
        int n = intervals.size();
        sort(intervals.begin(), intervals.end());
        int st = -1e9, ed = -1e9;

        for(int i = 0; i < n; i ++ ) {
            if(intervals[i][0] > ed) {
                if(ed != -1e9) ans.push_back({st, ed});
                st = intervals[i][0], ed = intervals[i][1];
            }
            ed = max(ed, intervals[i][1]);
        }
        ans.push_back({st, ed});
        return ans;
    }
};

189 轮转数组

方法一：

class Solution {
public:
// 直接模拟的做法，复杂度 o(N)
    void rotate(vector<int>& nums, int k) {
        int n = nums.size();
        vector<int> a(n);
        for(int i = 0; i < n; i ++ ) {
            a[(i + k) % n] = nums[i];
        }
        nums = a;
    }
};

方法二：

class Solution {
public:
// 原地算法，旋转数组，制定起始位置的数组旋转一下即可
    void reverse(vector<int>& nums, int start, int end) {
        while (start < end) {
            swap(nums[start], nums[end]);
            start += 1;
            end -= 1;
        }
    }

    void rotate(vector<int>& nums, int k) {
        k %= nums.size();
        reverse(nums, 0, nums.size() - 1);
        reverse(nums, 0, k - 1);
        reverse(nums, k, nums.size() - 1);
    }
};

238 除自身以外的数的乘积

class Solution {
public:
    vector<int> productExceptSelf(vector<int>& nums) {
        int n = nums.size();
        vector<int> ans(n), l(n), r(n);
        l[0] = 1;
        r[n - 1] = 1;
        for(int i = 1; i < n; i ++ ) {
            l[i] = l[i - 1] * nums[i - 1];
        }
        for(int i = n - 2; i >= 0; i -- ) {
            r[i] = r[i + 1] * nums[i + 1];
        }
        for(int i = 0; i < n; i ++ ) {
            ans[i] = l[i] * r[i];
        }
        return ans;
    }
};

41 缺失的第一个正数

// TODO

class Solution {
public:
    int firstMissingPositive(vector<int>& nums) {
        int n = nums.size();
        unordered_map<int, int> mp;
        for(auto x : nums) mp[x] = 1;
        int ans = -1;
        for(int i = 1; i ; i ++ ) {
            if(mp[i] == 0) {
                ans = i;
                break;
            }
        } 
        return ans;
    }
};