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

using namespace std;

const int maxn = 20009;

int a[maxn], t, n, d, tot;
int p[maxn], pn, cnt0[maxn], cnt1[maxn];
bool F[maxn];

void Init() {
memset(F, 0, sizeof F);
pn = 0;
for(int i = 2; i < maxn; i++) {
if(!F[i])
p[pn++] = i;
for(int j = 0; i * p[j] < maxn; j++) {
F[i * p[j]] = true;
if(i % p[j] == 0) break;
}
}
}

int buf[10000];
void calc(int h[]) {
memset(buf, 0, sizeof buf);
buf[0] = 1;
int L = 1;
for(int i = 0; i < pn; i++)
for(int j = 0; j < h[i]; j++) {
for(int k = 0; k < L; k++) buf[k] *= p[i];
for(int k = 0; k < L; k++) if(buf[k] > 9) {
buf[k + 1] += buf[k] / 10;
buf[k] %= 10;
}
for(; buf[L] > 0; L++) if(buf[L] > 9) {
buf[L + 1] += buf[L] / 10;
buf[L] %= 10;
}
}
while(L--)
putchar(buf[L] + '0');
}

void mult(int x, int h[]) {
for(int i = 0; i < pn; i++) if(x % p[i] == 0)
for(; x % p[i] == 0; x /= p[i]) h[i]++;
}

int main() {

Init();
scanf("%d%d%d", &t, &n, &d);
for(int i = 1; i <= t; i++) {
scanf("%d", a + i);
tot += a[i];
}
while(n--) {
int x, y;
scanf("%d%d", &x, &y);
mult(a[y], cnt0);
mult(tot, cnt1);
tot += d, a[y] += d;
}
for(int i = 0; i < pn; i++) if(cnt1[i] >= cnt0[i])
cnt1[i] -= cnt0[i], cnt0[i] = 0;
else if(cnt1[i] < cnt0[i])
cnt0[i] -= cnt1[i], cnt1[i] = 0;
calc(cnt0);
putchar('/');
calc(cnt1);

return 0;
}

http://www.cnblogs.com/JSZX11556/p/5184593.html 高精度

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