这是全部代码

#include <cstdio>
#include <cstring>
#include <algorithm>

using namespace std;

#define R register
#define LL long long
const int inf = 0x3f3f3f3f;
const int N = 2e6 + 10;

inline int read() {
	char a = getchar(); int x = 0,f = 1;
	for(;a > '9' || a < '0';a = getchar()) if(a == '-') f = -1;
	for(;a >= '0' && a <= '9'; a = getchar()) x = x * 10 + a - '0';
	return x * f;
}

int n, m = 128;
char s[N];
int x[N], y[N], c[N], sa[N];

inline void qsort() {
	for(R int i = 1; i <= m; i ++) c[i] = 0;
	for(R int i = 1; i <= n; i ++) c[x[i]] ++;
	for(R int i = 2; i <= m; i ++) c[i] += c[i - 1];
	for(R int i = n; i >= 1; i --) sa[c[x[y[i]]] --] = y[i], y[i] = 0;
}

int main() {
	freopen("a.in","r",stdin);
	scanf("%s", s + 1); n = strlen(s + 1);
	for(R int i = 1; i <= n; i ++) x[i] = s[i], y[i] = i;
	qsort();
	for(R int k = 1; k <= n; k = k << 1) {
		int num = 0;
		for(R int i = n - k + 1; i <= n; i ++) y[++ num] = i;
		for(R int i = 1; i <= n; i ++)
			if(sa[i] > k) y[++ num] = sa[i] - k;
		qsort(); swap(x, y);
		num = 1; x[sa[1]] = 1;
		for(R int i = 2; i <= n; i ++) 
			if(y[sa[i]] == y[sa[i - 1]] && y[sa[i] + k] == y[sa[i - 1] + k]) x[sa[i]] = num;
			else x[sa[i]] = ++ num;
		if(num == n) break;
		m = num;
	}
	for(R int i = 1; i <= n; i ++) printf("%d ", sa[i]); putchar('\n');
	return 0;	
}

请问

for(R int i = n; i >= 1; i --) sa[c[x[y[i]]] --] = y[i], y[i] = 0;

和

for(R int i = n - k + 1; i <= n; i ++) y[++ num] = i;
		for(R int i = 1; i <= n; i ++)
			if(sa[i] > k) y[++ num] = sa[i] - k;

到底啥意思 ？