NOIP 2010 普及组 数字统计

#include using namespace std;int l, r, cnt = 0;int main() {cin >> l >> r;for (int i = l; i <= r; i ++ ) {int t = i;while (t) {if (t % 10 == 2) cnt ++ ;t /= 10;}}cout << cnt;return 0;}

#include using namespace std;int l, r, cnt = 0;int f[10000];int main() {cin >> l >> r;for (int i = 0; i < 1000; i ++) {for (int j = 0; j < 10; j ++) {f[i * 10 + j] = f[i] + (j == 2);}}for (int i = l; i <= r; i ++) cnt += f[i];cout << cnt;return 0;}