Permutacja (SPOJ AE5B2)

#include <iostream>
#include <cstdio>
#include <cstring>
using namespace std;
const int MAXN = 262144;
// stores binary tree in [1..2*MAXN-1], the leaves are [MAXN..2*MAXN-1]
// assumes MAXN is a power of 2. functions act on [x..y]
const int INF = 0x3f3f3f3f;
int a[2*MAXN], b[2*MAXN];
inline int update(int y, int v, int i=1, int l=0, int r=MAXN-1) {
    if (y<l) return a[i];
    if (l==r) return a[i] += v;
    if (r <= y) {
        b[i] += v;
        return a[i]+b[i];
    }
    int m = (l+r)/2;
    if (b[i]) {
        b[2*i] += b[i];
        b[2*i+1] += b[i];
        b[i] = 0;
    }
    if(y < m) update(y,v,2*i,l,m);
    else {
        b[2*i] += v;
        update(y,v,2*i+1,m+1,r);
    }
    a[i] = min(a[2*i]+b[2*i], a[2*i+1]+b[2*i+1]);
}
int main() {
    int n; scanf("%d", &n);
    memset(a, INF, sizeof a); memset(b, 0, sizeof b);
    for (int i=0; i < n; i++) a[MAXN+i] = i-n;
    for (int i=MAXN-1; i >= 1; i--) a[i] = min(a[2*i], a[2*i+1]);

    int z[n+1];
    for (int i=1; i <= n; i++) {
        scanf("%d", z+i);
        update(z[i]-1, 1);
    }

    printf("%s\n", a[1] < 0 ? "NIE" : "TAK");
    int m; scanf("%d", &m);
    while(m--) {
        int j, w; scanf("%d %d", &j, &w);
        update(z[j]-1, -1);
        update(w-1, 1);
        z[j] = w;
        printf("%s\n", a[1] < 0 ? "NIE" : "TAK");
    }
    return 0;
}