74 lines
2.6 KiB
C++
74 lines
2.6 KiB
C++
#include <vector>
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#include <cstdio>
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/**
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* 421. Maximum XOR of Two Numbers in an Array
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* Given an integer array nums, return the maximum result of nums[i] XOR nums[j], where 0 <= i <= j < n.
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*/
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class Solution {
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private:
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static const int bpoBits = 3;
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static const int bitsPerOperation = 1 << bpoBits;
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inline static constexpr int getBits(int n, int b) {
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return (n >> (b << bpoBits)) & ((1 << bitsPerOperation) - 1);
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}
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public:
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// (32 / bitsPerOperation) * n + (2 ^ bitsPerOperation) ^ 2
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static int findMaximumXOR(const std::vector<int>& nums) {
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std::vector<int> bucket[2][1 << bitsPerOperation];
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std::vector<std::pair<std::vector<int>, std::vector<int>>> pool[2]{{{nums, nums}}, {}};
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for (int i = 32 / bitsPerOperation - 1; i >= 0; --i) {
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auto& thisPool = pool[1 & i];
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const auto& thatPool = pool[1 ^ (1 & i)];
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thisPool.clear();
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int maxVal = -1;
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// For any pair of sequences which can pair...
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for (const auto& pair : thatPool) {
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// Clear bucket
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for (auto& j : bucket)
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for (auto& k : j)
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k.clear();
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// Construct bucket
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for (auto& j : pair.first)
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bucket[0][getBits(j, i)].push_back(j);
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for (auto& j : pair.second)
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bucket[1][getBits(j, i)].push_back(j);
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// Find the max possible xor of this pair...
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int thisMax = -1;
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for (int j = 0; j < (1 << bitsPerOperation); ++j) {
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if (bucket[0][j].empty())
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continue;
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for (int k = 0; k < (1 << bitsPerOperation); ++k)
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if (!bucket[1][k].empty() && (j ^ k) > thisMax)
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thisMax = j ^ k;
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}
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// Only the strongest could survive!
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if (thisMax >= maxVal) {
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if (thisMax > maxVal) {
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thisPool.clear();
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maxVal = thisMax;
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}
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// Anything in that pool has the maximum possible xor for processed bits.
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// This pool should be the same.
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for (int j = 0; j < (1 << bitsPerOperation); ++j) {
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if (bucket[0][j].empty() || bucket[1][thisMax ^ j].empty())
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continue;
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thisPool.emplace_back(bucket[0][j], bucket[1][thisMax ^ j]);
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}
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}
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}
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}
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return pool[0][0].first[0] ^ pool[0][0].second[0];
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}
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};
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int main() {
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std::printf("%d\n", Solution::findMaximumXOR({2604,6991,8010,8260,5136,8770,8568,3021,1621,7303,9289,9855,7267,7872,1163,2605,1438,5683,7245,3647,7977,2361,8355,3215,1784,1189,9334,4099,2467,9342,5512,2823,1254,6315,645,3638,5077,8442,5957,501,8045,1790,7357,7180,8614,2899,3222,2994,228,5662,8421,7060,669,9413,9353,9697,9141,3688,580,8309,7285,4091,9712,3296,5322,7490,4899,6083,9961,2392,685,1862,5664,2667,6414,2888,3624,5495,4677,2932,9942,6013,1235,6733,8609,5504,9181,6886,7822,2125,4800,1760,8632,468,4927,3009,7627,4167,4296,5437}));
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return 0;
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}
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