RandomShuffle.h

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// Copyright Epic Games, Inc. All Rights Reserved.
 
#pragma once
 
#include "Math/UnrealMathUtility.h"
#include "Templates/UnrealTemplate.h"
 
namespace Algo
{
    /**
     * Randomly shuffle a range of elements.
     *
     * @param  Range  Any contiguous container.
     */
    template <typename RangeType>
    void RandomShuffle(RangeType& Range)
    {
        auto Data = GetData(Range);
 
        using SizeType = decltype(GetNum(Range));
        const SizeType Num = GetNum(Range);
 
        for (SizeType Index = 0; Index < Num - 1; ++Index)
        {
            // Get a random integer in [Index, Num)
            const SizeType RandomIndex = Index + (SizeType)FMath::RandHelper64(Num - Index);
            if (RandomIndex != Index)
            {
                Swap(Data[Index], Data[RandomIndex]);
            }
        }
    }
}