# 789. Escape The Ghosts 逃脱阻碍者

@TOC

## # 题目描述

You are playing a simplified Pacman game. You start at the point `(0, 0)`, and your destination is `(target[0], target[1])`. There are several ghosts on the map, the i-th ghost starts at `(ghosts[i][0], ghosts[i][1])`.

Each turn, you and all ghosts simultaneously `*may*` move in one of 4 cardinal directions: north, east, west, or south, going from the previous point to a new point 1 unit of distance away.

You escape if and only if you can reach the target before any ghost reaches you (for any given moves the ghosts may take.) If you reach any square (including the target) at the same time as a ghost, it doesn't count as an escape.

Return True if and only if it is possible to escape.

Example 1:

``````Input:
ghosts = [[1, 0], [0, 3]]
target = [0, 1]
Output: true
Explanation:
You can directly reach the destination (0, 1) at time 1, while the ghosts located at (1, 0) or (0, 3) have no way to catch up with you.
``````

Example 2:

``````Input:
ghosts = [[1, 0]]
target = [2, 0]
Output: false
Explanation:
You need to reach the destination (2, 0), but the ghost at (1, 0) lies between you and the destination.
``````

Example 3:

``````Input:
ghosts = [[2, 0]]
target = [1, 0]
Output: false
Explanation:
The ghost can reach the target at the same time as you.
``````

Note:

1. All points have coordinates with absolute value <= 10000.
2. The number of ghosts will not exceed 100.

## # 解题方法

``````class Solution:
def escapeGhosts(self, ghosts, target):
"""
:type ghosts: List[List[int]]
:type target: List[int]
:rtype: bool
"""
mht = sum(map(abs, target))
tx, ty = target
return not any(abs(gx - tx) + abs(gy - ty) <= mht for gx, gy in ghosts)
``````

C++代码如下：

``````class Solution {
public:
bool escapeGhosts(vector<vector<int>>& ghosts, vector<int>& target) {
int time = distance({0, 0}, target);
for (auto g : ghosts) {
if (distance(g, target) <= time)
return false;
}
return true;
}
private:
int distance(vector<int> source, vector<int>& target) {
return abs(target[0] - source[0]) + abs(target[1] - source[1]);
}
};
``````

## # 日期

2018 年 5 月 28 日 ———— 太阳真的像日光灯～ 2018 年 12 月 11 日 —— 双十一已经过去一个月了，真快啊。。