# 数位 DP 入门：HDU 3555 Bomb

## HDU 3555 Bomb

The counter-terrorists found a time bomb in the dust. But this time the terrorists improve on the time bomb. The number sequence of the time bomb counts from 1 to N. If the current number sequence includes the sub-sequence "49", the power of the blast would add one point.
Now the counter-terrorist knows the number N. They want to know the final points of the power. Can you help them?

More...

# gdb 调试的使用

Linux 下没有 Dev-cpp，每次遇到想要调试的代码就是坠痛苦的。所以我们还是得学点 gdb 调试的命令。

More...

More...

More...

# POJ 3465 Battle 题解：可“反悔”的贪心

## Description

You're Zhu Rengong, a formidable hero. After a number of challenging missions, you are finally facing the final Boss – a black dragon called Heilong. Due to his overwhelming power, you have to plan your actions carefully.

More...

# POJ 3244 Difference between Triplets 题解：（线段树或树状数组）或（排序 + 前缀和）

## Description

For every pair of triplets, $T_a = (I_a, J_a, K_a)$ and $T_b = (I_b, J_b, K_b)$, we define the difference value between $T_a$ and $T_b$ as follows:

$$D(T_a, T_b) = \max (I_a − I_b, J_a − J_b, K_a − K_b) − \min (I_a − I_b, J_a − J_b, K_a − K_b)$$

Now you are given $N$ triplets, could you write a program to calculate the sum of the difference values between every unordered pair of triplets?

More...

More...

# HDU 6447 YJJ's Salesman 题解：排序+离散+树状数组

## Problem Description

YJJ is a salesman who has traveled through western country. YJJ is always on journey. Either is he at the destination, or on the way to destination.
One day, he is going to travel from city $A$ to southeastern city $B$. Let us assume that A is $(0,0)$ on the rectangle map and $B (10^9,10^9)$. YJJ is so busy so he never turn back or go twice the same way, he will only move to east, south or southeast, which means, if YJJ is at $(x,y)$ now $(0\leqslant x\leqslant 10^9,0\leqslant y\leqslant 10^9)$, he will only forward to $(x+1,y)$, $(x,y+1)$ or $(x+1,y+1)$.

More...

More...