a binary search / 二分探索
(utils/binary_search.hpp)

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• Last update: 2019-12-15 04:15:59+09:00
• Include: #include "utils/binary_search.hpp"

Verified with

• utils/binary_search.aoj.test.cpp

Code

#pragma once
#include <cassert>
#include <cstdint>

/**
 * @brief a binary search / 二分探索
 * @param[in] p  a monotone predicate defined on $[l, r)$
 * @return $\min \lbrace x \in [l, r) \mid p(x) \rbrace$, or r if it doesn't exist
 */
template <typename UnaryPredicate>
int64_t binsearch(int64_t l, int64_t r, UnaryPredicate p) {
    assert (l <= r);
    -- l;
    while (r - l > 1) {
        int64_t m = l + (r - l) / 2;
        (p(m) ? r : l) = m;
    }
    return r;
}

/**
 * @return $\max \lbrace x \in (l, r] \mid p(x) \rbrace$, or l if it doesn't exist
 */
template <typename UnaryPredicate>
int64_t binsearch_max(int64_t l, int64_t r, UnaryPredicate p) {
    assert (l <= r);
    ++ r;
    while (r - l > 1) {
        int64_t m = l + (r - l) / 2;
        (p(m) ? l : r) = m;
    }
    return l;
}

#line 2 "utils/binary_search.hpp"
#include <cassert>
#include <cstdint>

/**
 * @brief a binary search / 二分探索
 * @param[in] p  a monotone predicate defined on $[l, r)$
 * @return $\min \lbrace x \in [l, r) \mid p(x) \rbrace$, or r if it doesn't exist
 */
template <typename UnaryPredicate>
int64_t binsearch(int64_t l, int64_t r, UnaryPredicate p) {
    assert (l <= r);
    -- l;
    while (r - l > 1) {
        int64_t m = l + (r - l) / 2;
        (p(m) ? r : l) = m;
    }
    return r;
}

/**
 * @return $\max \lbrace x \in (l, r] \mid p(x) \rbrace$, or l if it doesn't exist
 */
template <typename UnaryPredicate>
int64_t binsearch_max(int64_t l, int64_t r, UnaryPredicate p) {
    assert (l <= r);
    ++ r;
    while (r - l > 1) {
        int64_t m = l + (r - l) / 2;
        (p(m) ? l : r) = m;
    }
    return l;
}

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