【HDOJ】1597 find the nth digit

二分。

#include <stdio.h>
#include <math.h>

int main() {
    int case_n;
    double n, tmp, l, r;
    int m;

    scanf("%d", &case_n);

    while (case_n--) {
        scanf("%lf", &n);
        tmp = sqrt(n+n);
        tmp = ceil(tmp);
        l = (tmp*tmp-tmp)/2;
        r = (tmp*tmp+tmp)/2;
        while ( !(l<n && r>=n) ) {
            --tmp;
            l = (tmp*tmp-tmp)/2;
            r = (tmp*tmp+tmp)/2;
        }
        m = (int)(n-l);
        m %= 9;
        if (m==0) m=9;
        printf("%d
", m);
    }

    return 0;
}