題目

歸并排序

思路

和快排一樣，先判斷數據是否沒有或者只為一個；如果大于一個，取中間的值一分為二，然后兩邊遞歸，歸并的實質是把兩個有序數組排成一個，兩個數組都從頭開始比較，把更小的取下放到數組temp中，指針后移，最后再把temp數組全部賦值給a數組。

代碼

#include<iostream>
using namespace std;
const int N = 100010;
int n;
int a[N], temp[N];
void merge_sort(int a[], int l, int r)
{if (l >= r){return;}int mid = (l + r) / 2;merge_sort(a, l, mid), merge_sort(a, mid + 1, r);int k = 0, i = l, j = mid + 1;while (i <= mid && j <= r){if (a[i] <= a[j]){temp[k++] = a[i++];}else{temp[k++] = a[j++];}}while (i <= mid){temp[k++] = a[i++];}while (j <= r){temp[k++] = a[j++];}for (int i = l, j = 0;i <= r;i++, j++){a[i] = temp[j];}
}
int main()
{cin >> n;for (int i = 0;i < n;i++){cin >> a[i];}merge_sort(a, 0, n - 1);for (int i = 0;i < n;i++){cout << a[i] << " ";}return 0;
}