LeetCode-Solutions/C++/threshold-majority-queries.cpp at master · kamyu104/LeetCode-Solutions · GitHub

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
// Time:  O(nlogn + qlogq + (n + q) * sqrt(n) + q * n)
// Space: O(n + q)

// sort, coordinate compression, mo's algorithm
class Solution {
public:
    vector<int> subarrayMajority(vector<int>& nums, vector<vector<int>>& queries) {
        vector<int> sorted_nums(nums);
        sort(begin(sorted_nums), end(sorted_nums));
        sorted_nums.erase(unique(begin(sorted_nums), end(sorted_nums)), end(sorted_nums));
        unordered_map<int, int> num_to_idx;
        for (int i = 0; i < size(sorted_nums); ++i) {
            num_to_idx[sorted_nums[i]] = i;
        }

        // reference: https://cp-algorithms.com/data_structures/sqrt_decomposition.html
        const auto& mo_s_algorithm = [&]() {
            vector<int> cnt(size(num_to_idx));
            vector<int> cnt2(size(nums) + 1);
            int max_freq = 0;
            const auto& add = [&](int i) {
                const auto& idx = num_to_idx[nums[i]];
                if (cnt[idx]) {
                    --cnt2[cnt[idx]];
                }
                ++cnt[idx];
                ++cnt2[cnt[idx]];
                max_freq = max(max_freq, cnt[idx]);
            };

            const auto& remove = [&](int i) {
                const auto& idx = num_to_idx[nums[i]];
                --cnt2[cnt[idx]];
                if (!cnt2[max_freq]) {
                    --max_freq;
                }
                --cnt[idx];
                if (cnt[idx]) {
                    ++cnt2[cnt[idx]];
                }
            };

            const auto& get_ans = [&](int t) {
                if (max_freq < t) {
                    return -1;
                }
                int i = 0;
                for (; i < size(cnt); ++i) {
                    if (cnt[i] == max_freq) {
                        break;
                    }
                }
                return sorted_nums[i];
            };

            vector<int> result(size(queries), -1);
            const int block_size = sqrt(size(nums)) + 1;
            vector<int> idxs(size(queries));
            iota(begin(idxs), end(idxs), 0);
            sort(begin(idxs), end(idxs), [&](const auto& a, const auto& b) {
                const auto& i = queries[a][0] / block_size;
                const auto& j = queries[b][0] / block_size;
                return i != j ? i < j : (i & 1 ? queries[a][1] < queries[b][1] : queries[a][1] > queries[b][1]);
            });
            int left = 0, right = -1;
            for (const auto& i : idxs) {
                const auto& l = queries[i][0];
                const auto& r = queries[i][1];
                const auto& t = queries[i][2];
                while (left > l) {
                    left -= 1;
                    add(left);
                }
                while (right < r) {
                    ++right;
                    add(right);
                }
                while (left < l) {
                    remove(left);
                    ++left;
                }
                while (right > r) {
                    remove(right);
                    --right;
                }
                result[i] = get_ans(t);
            }
            return result;
        };

        return mo_s_algorithm();
    }
};

// Time:  O(nlogn + qlogq + (n + q) * sqrt(n) * logn)
// Space: O(n + q)
// sort, coordinate compression, mo's algorithm, bst
class Solution2 {
public:
    vector<int> subarrayMajority(vector<int>& nums, vector<vector<int>>& queries) {
        vector<int> sorted_nums(nums);
        sort(begin(sorted_nums), end(sorted_nums));
        sorted_nums.erase(unique(begin(sorted_nums), end(sorted_nums)), end(sorted_nums));
        unordered_map<int, int> num_to_idx;
        for (int i = 0; i < size(sorted_nums); ++i) {
            num_to_idx[sorted_nums[i]] = i;
        }

        // reference: https://cp-algorithms.com/data_structures/sqrt_decomposition.html
        const auto& mo_s_algorithm = [&]() {
            vector<int> cnt(size(num_to_idx));
            vector<multiset<int>> lookup(size(nums) + 1);
            int max_freq = 0;
            const auto& add = [&](int i) {
                const auto& idx = num_to_idx[nums[i]];
                if (cnt[idx]) {
                    auto it = lookup[cnt[idx]].find(nums[i]);
                    lookup[cnt[idx]].erase(it);
                }
                ++cnt[idx];
                lookup[cnt[idx]].emplace(nums[i]);
                max_freq = max(max_freq, cnt[idx]);
            };

            const auto& remove = [&](int i) {
                const auto& idx = num_to_idx[nums[i]];
                auto it = lookup[cnt[idx]].find(nums[i]);
                lookup[cnt[idx]].erase(it);
                if (empty(lookup[max_freq])) {
                    --max_freq;
                }
                --cnt[idx];
                if (cnt[idx]) {
                    lookup[cnt[idx]].emplace(nums[i]);
                }
            };

            const auto& get_ans = [&](int t) {
                return max_freq >= t ? *begin(lookup[max_freq]) : -1;
            };

            vector<int> result(size(queries), -1);
            const int block_size = sqrt(size(nums)) + 1;
            vector<int> idxs(size(queries));
            iota(begin(idxs), end(idxs), 0);
            sort(begin(idxs), end(idxs), [&](const auto& a, const auto& b) {
                const auto& i = queries[a][0] / block_size;
                const auto& j = queries[b][0] / block_size;
                return i != j ? i < j : (i & 1 ? queries[a][1] < queries[b][1] : queries[a][1] > queries[b][1]);
            });
            int left = 0, right = -1;
            for (const auto& i : idxs) {
                const auto& l = queries[i][0];
                const auto& r = queries[i][1];
                const auto& t = queries[i][2];
                while (left > l) {
                    left -= 1;
                    add(left);
                }
                while (right < r) {
                    ++right;
                    add(right);
                }
                while (left < l) {
                    remove(left);
                    ++left;
                }
                while (right > r) {
                    remove(right);
                    --right;
                }
                result[i] = get_ans(t);
            }
            return result;
        };

        return mo_s_algorithm();
    }
};