LeetCode/4Sum.cpp at master · Riddance/LeetCode · 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
//will TLE
class Solution {
public:
    vector<vector<int> > fourSum(vector<int> &num, int target) {
        std::vector<std::vector<int> > rv;

        if ((int)num.size() < 4) {
            return rv;
        }

        struct ValPair{
            int index1;
            int index2;
        };

        std::multimap<int, ValPair, std::less<int> > SumToPair;
        for (int i = 0; i < (int)num.size() - 1; ++i) {
            for (int j = i + 1; j < (int)num.size(); ++j) {

                ValPair ijPair;
                ijPair.index1 = i;
                ijPair.index2 = j;
                int ijSum = num[i] + num[j];

                SumToPair.insert(make_pair(ijSum, ijPair));
            }
        }

        assert(SumToPair.size() > 2);

        using SUM_TO_PAIR_ITER = decltype(SumToPair.begin());
        std::vector<SUM_TO_PAIR_ITER> VecIter;

        auto Iter = SumToPair.begin();

        while (Iter != SumToPair.end()) {
            VecIter.push_back(Iter);
            ++Iter;
        }

        std::vector<int> r(4, 0);

        for (int i = 0; i < (int)VecIter.size() - 1; ++i) {
            for (int j = i + 1; j < (int)VecIter.size(); ++j) {
                auto lhs = VecIter[i];
                auto rhs = VecIter[j];

                if (
                    lhs->second.index1 == rhs->second.index1 ||
                    lhs->second.index1 == rhs->second.index2 ||
                    lhs->second.index2 == rhs->second.index1 ||
                    lhs->second.index2 == rhs->second.index2
                ) {
                    continue;
                }

                int sumPairs = lhs->first + rhs->first;

                if (sumPairs != target) {
                    continue;
                }

                r[0] = num[lhs->second.index1];
                r[1] = num[lhs->second.index2];
                r[2] = num[rhs->second.index1];
                r[3] = num[rhs->second.index2];

                std::sort(r.begin(), r.end(), std::less<int>());

                if (std::find(rv.begin(), rv.end(), r) == rv.end()) {
                    rv.push_back(r);
                }
            }
        }

        return rv;
    }
};

class Solution {
public:
    vector<vector<int> > fourSum(vector<int> &num, int target) {
        std::vector<std::vector<int> > rv;
        std::vector<int> r(4, 0);

        if (num.size() < 4) {
            return rv;
        }

        std::sort(num.begin(), num.end(), std::less<int>());

        for (int i = 0; i < (int)num.size() - 1; ++i) {

            if (i != 0 && num[i] == num[i - 1]) {
                continue;
            }

            for (int j = i + 1; j < (int)num.size(); ++j) {
                int lhs = j + 1;
                int rhs = num.size() - 1;

                if (j != i + 1 && num[j] == num[j - 1]) {
                    continue;
                }

                while (lhs < rhs) {

                    if (lhs != j + 1 && num[lhs] == num[lhs - 1]) {
                        ++lhs;
                        continue;
                    }

                    int sum4 = num[i] + num[j] + num[lhs] + num[rhs];
                    if (sum4 == target) {
                        r[0] = num[i];
                        r[1] = num[j];
                        r[2] = num[lhs];
                        r[3] = num[rhs];

                        rv.push_back(r);

                        ++lhs;
                        --rhs;
                    }
                    else if (sum4 < target) {
                        ++lhs;
                    }
                    else {
                        --rhs;
                    }
                }
            }
        }

        return rv;
    }
};