快速排序

算法证明及边界问题的考虑

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#include<bits/stdc++.h>
using namespace std;

void quick_sort(vector<int> &a, int l, int r) {
    if(l >= r - 1) {
        return;
    }
    int x = a[(l + r - 1) / 2], i = l - 1, j = r;
    while(i < j) {
        do i ++;
        while (a[i] < x);
        do j--;
        while (a[j] > x);
        if(i < j) {
            swap(a[i], a[j]);
        }
    }
    quick_sort(a, l, j + 1);
    quick_sort(a, j + 1, r);
}

int main() {
    int n;
    cin >> n;
    vector<int> a(n);
    for (int i = 0; i < n; i ++ ) {
        cin >> a[i];
    }
    quick_sort(a, 0, n);
    for (int i = 0; i < n; i ++ ) {
        cout << a[i] << " ";
    }
    return 0;
}

归并排序

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#include<bits/stdc++.h>
using namespace std;

void merge_sort(vector<int> &a, int l, int r) {
    if(l >= r - 1) {
        return;
    }
    int mid = l + r >> 1;
    merge_sort(a, l, mid), merge_sort(a, mid, r);
    vector<int> temp(r - l + 1);
    int p = 0, i = l, j = mid;
    while(i < mid && j < r) {
        if(a[i] < a[j]) {
            temp[p++] = a[i++];
        } else {
            temp[p++] = a[j++];
        }
    }
    while(i < mid) {
        temp[p++] = a[i++];
    }
    while(j < r) {
        temp[p++] = a[j++];
    }
    for (int i = l; i < r; i ++ ) {
        a[i] = temp[i - l];
    }
}

int main() {
    int n;
    cin >> n;
    vector<int> a(n);
    for(int i = 0; i < n; i ++ ) {
        cin >> a[i];
    }
    merge_sort(a, 0, n);
    for(int i = 0; i < n; i ++ ) {
        cout << a[i] << " ";
    }
    return 0;
}