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select.cpp
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select.cpp
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/*
* Copyright 2018 Google LLC
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* https://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#include <stdint.h>
#include <algorithm>
#include <vector>
#include "randbelow.h"
extern "C" void random_select(uint32_t n, uint32_t k, uint32_t* result) {
std::vector<uint32_t> options(n);
for (uint32_t i = 0; i < n; i++) {
options[i] = i;
}
for (uint32_t i = 0; i < k; i++) {
uint32_t r = i + randbelow(n - i);
result[i] = options[r];
options[r] = options[i];
}
}
extern "C" void sorted_select(uint32_t n, uint32_t k, uint32_t* result) {
random_select(n, k, result);
std::sort(result, result + k);
}