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absent_value_array.cc
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absent_value_array.cc
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#include <bitset>
#include <stdexcept>
#include <vector>
#include "test_framework/generic_test.h"
#include "test_framework/test_failure.h"
using std::bitset;
using std::invalid_argument;
using std::vector;
int FindMissingElement(vector<int>::const_iterator stream_begin,
const vector<int>::const_iterator& stream_end) {
const int kNumBucket = 1 << 16;
vector<size_t> counter(kNumBucket, 0);
vector<int>::const_iterator stream_begin_copy = stream_begin;
while (stream_begin != stream_end) {
int upper_part_x = *stream_begin >> 16;
++counter[upper_part_x];
++stream_begin;
}
// Look for a bucket that contains less than (1 << 16) elements.
const int kBucketCapacity = 1 << 16;
int candidate_bucket;
for (int i = 0; i < kNumBucket; ++i) {
if (counter[i] < kBucketCapacity) {
candidate_bucket = i;
break;
}
}
// Finds all IP addresses in the stream whose first 16 bits
// are equal to candidate_bucket.
bitset<kBucketCapacity> candidates;
stream_begin = stream_begin_copy;
while (stream_begin != stream_end) {
int x = *stream_begin++;
if (int upper_part_x = x >> 16; candidate_bucket == upper_part_x) {
// Records the presence of 16 LSB of x.
int lower_part_x = ((1 << 16) - 1) & x;
candidates.set(lower_part_x);
}
}
// At least one of the LSB combinations is absent, find it.
for (int i = 0; i < kBucketCapacity; ++i) {
if (candidates[i] == 0) {
return (candidate_bucket << 16) | i;
}
}
throw invalid_argument("no missing element");
}
int FindMissingElementWrapper(const vector<int>& stream) {
try {
return FindMissingElement(cbegin(stream), cend(stream));
} catch (invalid_argument&) {
throw TestFailure("Unexpected no_missing_element exception");
}
}
int main(int argc, char* argv[]) {
std::vector<std::string> args{argv + 1, argv + argc};
std::vector<std::string> param_names{"stream"};
return GenericTestMain(args, "absent_value_array.cc",
"absent_value_array.tsv", &FindMissingElementWrapper,
DefaultComparator{}, param_names);
}