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68 lines
986 B
C++
68 lines
986 B
C++
/*
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Quick select algorithm
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Copyright 2024 Ahmet Inan <inan@aicodix.de>
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*/
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#pragma once
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namespace DSP {
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namespace QUICK {
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template <typename TYPE>
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static inline void swap(TYPE *a, int i, int j)
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{
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TYPE t = a[i];
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a[i] = a[j];
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a[j] = t;
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}
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template <typename TYPE>
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static inline void sort(TYPE *a, int i, int j, int k)
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{
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if (a[i] > a[j])
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swap(a, i, j);
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if (a[i] > a[k])
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swap(a, i, k);
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if (a[j] > a[k])
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swap(a, j, k);
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}
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template <typename TYPE>
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static int partition(TYPE *a, int l, int h)
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{
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sort(a, (l + h) / 2, h, l);
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for (int i = l; i < h; ++i)
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if (a[i] < a[h])
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swap(a, i, l++);
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swap(a, l, h);
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return l;
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}
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template <typename TYPE>
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static TYPE select(TYPE *a, int l, int h, int k)
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{
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while (l < h) {
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int i = partition(a, l, h);
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if (k == i)
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return a[k];
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if (k < i)
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h = i - 1;
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else
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l = i + 1;
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}
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return a[l];
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}
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}
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template <typename TYPE>
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TYPE quick_select(TYPE *a, int k, int n)
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{
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assert(n && k < n);
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return QUICK::select(a, 0, n-1, k);
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}
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}
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