又学会了骂人的新词语。
代码实现如下：
#include <bits/stdc++.h> using namespace std; #define rep(i, a, b) for (register int i = (a); i <= (b); i++) const int maxn = 10; int l, r, ans, len; int num[maxn], dp[maxn][maxn]; void origin() {memset(dp, -1, sizeof(dp));} int dfs(int pos, int limit, int lead, int is_six) { int ans = 0; if (!pos) return 1; if (!limit && !lead && dp[pos][is_six] != -1) return dp[pos][is_six]; int res = limit ? num[pos] : 9; rep(i, 0, res) { if (i == 4 || (is_six && i == 2)) continue; if (!i && lead) ans += dfs(pos - 1, (i == res) && limit, 0, i == 6); else ans += dfs(pos - 1, (i == res) && limit, 1, i == 6); } if (!limit && !lead) dp[pos][is_six] = ans; return ans; } int work(int x) { origin(); len = 0; while (x) { num[++len] = x % 10; x /= 10; } return dfs(len, 1, 1, 0); } void write(int x) { if (x < 0) { putchar('-'); x = -x; } if (x > 9) write(x / 10); putchar(x % 10 + '0'); } int main() { while (scanf("%d%d", &l, &r) && l && r) { write(work(r) - work(l - 1)); printf("\n"); } return 0; } 但实际上我更习惯顺着搜：
#include <bits/stdc++.h> using namespace std; #define rep(i, a, b) for (register int i = (a); i <= (b); i++) const int maxn = 10; int l, r, ans, len; int num[maxn], dp[maxn][maxn]; void origin() {memset(dp, -1, sizeof(dp));} int dfs(int pos, int limit, int lead, int is_six) { int ans = 0; if (pos > len) return 1; if (!limit && !lead && dp[pos][is_six] != -1) return dp[pos][is_six]; int res = limit ? num[len - pos + 1] : 9; rep(i, 0, res) { if (i == 4 || (is_six && i == 2)) continue; if (!i && lead) ans += dfs(pos + 1, (i == res) && limit, 0, i == 6); else ans += dfs(pos + 1, (i == res) && limit, 1, i == 6); } if (!limit && !lead) dp[pos][is_six] = ans; return ans; } int work(int x) { origin(); len = 0; while (x) { num[++len] = x % 10; x /= 10; } return dfs(1, 1, 1, 0); } void write(int x) { if (x < 0) { putchar('-'); x = -x; } if (x > 9) write(x / 10); putchar(x % 10 + '0'); } int main() { while (scanf("%d%d", &l, &r) && l && r) { write(work(r) - work(l - 1)); printf("\n"); } return 0; }