hdu 3183 A Magic Lamp(RMQ)

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

using namespace std;

const int maxn = 10005;

int N, M, d[maxn][20];
char s[maxn];

void rmq_init() {
N = strlen(s);
for (int i = 0; i < N; i++)
d[i][0] = s[i];
for (int k = 1; (1<<k) <= N; k++) {
for (int i = 0; i < N; i++)
d[i][k] = min(d[i][k-1], d[i+(1<<(k-1))][k-1]);
}
}

int rmq_query(int l, int r) {
int k = 0;
while ((1<<(k+1)) <= r - l + 1) k++;
return min(d[l][k], d[r-(1<<k)+1][k]);
}

int main () {
while (scanf("%s%d", s, &M) == 2) {
rmq_init();
M = N - M;

int mv = 0;
bool flag = true;

for (int i = M; i; i--) {
int c = rmq_query(mv, N - i);

while (mv < N && s[mv] != c) mv++;
mv++;

if (c == '0' && flag)
continue;

flag = false;
printf("%c", c);
}

if (flag)
printf("0");
printf("\n");
}
return 0;
}