邮局选址问题 - Xredman - 博客园


邮局选址问题 - Xredman - 博客园
在一个按照东西和南北方向划分成规整街区的城市里,n个居民点散乱地分布在不同的街区中。用x 坐标表示东西向,用y坐标表示南北向。各居民点的位置可以由坐标(x,y)表示。街区中任意2 点(x1,y1)和(x2,y2)之间的距离可以用数值|x1-x2|+|y1-y2|度量。居民们希望在城市中选择建立邮局的最佳位置,使n个居民点到邮局的距离总和最小。
编程任务:
给定n 个居民点的位置,编程计算n 个居民点到邮局的距离总和的最小值。

Input
输入由多组测试数据组成。
每组测试数据输入的第1 行是居民点数n,1≤n≤10000。接下来n 行是居民点的位置,每行2 个整数x 和y,-10000≤x,y≤10000。

Output
对应每组输入,输出的第1 行中的数是n 个居民点到邮局的距离总和的最小值。
Sample Input

5 1 2 2 2 1 3 3 -2 3 3


Sample Output

10
因为街区中任意2 点(x1,y1)和(x2,y2)之间的距离可以用数值 |x1-x2 |+ |y1-y2 |度量;
那么:
邮局的x坐标只与n个居民点的x坐标相关;
邮局的y 坐标只与n个居民点的y坐标相关;

下面以求x坐标为例,y坐标的求法类似;

假设对n个居民点的x坐标按大小排序后为x1,x2....xi...xn;

对x1,xn两点来说,最近的点肯定在x1,xn之间,且跟两点的距离和==xn-x1;
对x2,x(n-1)两点来说,最近的点肯定在x2,x(n-1)之间,且跟两点的距离和==x(n-1)-x2;
....

所以若n为奇数,则邮局的x坐标取最中间的值时最小;
所以若n为偶数,则邮局的x坐标可以取最中间两个值的之间的任意值;

最终公式:x=(x(n/2+1)+x(n/2+2)+...+xn)-(x1+x2+..+x(n/2))

最终公式:
s=(x(n/2+1)+x(n/2+2)+...+xn)-(x1+x2+..+x(n/2))
+(y(n/2+1)+y(n/2+2)+...+yn)-(y1+y2+..+y(n/2))

bool cmp(int a, int b)
{
    
if(a < b)
        
return true;
    
else
        
return false;
}


int cal(int str[], int n)
{
    
int sum = 0,i,mid;
    mid 
= str[n / 2];
    
for(i = 0; i < n; i++)
        sum 
+= abs(str[i] - mid);
    
return sum;
}


int main()
{
    
int x[MAX_SIZE],y[MAX_SIZE];
    
int i, n;
    
while(scanf("%d",&n) != EOF)
    
{
        
for(i = 0; i < n; i++)
            scanf(
"%d%d",x + i, y + i);
        sort(x ,x 
+ n, cmp);
        sort(y, y 
+ n, cmp);
        printf(
"%d\n",cal(x, n) + cal(y, n));
    }

    
return 0;
}

http://segmentfault.com/a/1190000000636173
因为任意2 点(x1,y1)和(x2,y2)之间的距离是用数值|x1-x2|+|y1-y2|度量的,那么n个点P1----Pn到邮局地点P(x,y)的距离之和可以表示为: |x1-x|+ |x2-x|+……+|xn-x| + |y1-y|+ |y2-y|+……+|yn-y| 。
这样一来,问题转变为分别求x轴和y轴上的一个点,使得该轴上的其他点坐标与该点坐标的差的绝对值之和最小。
于是问题就变为求解中位数。因为给定一个数列,中位数有这样的性质 :所有数与中位数的绝对差之和最小。
下面给出简略证明(因为如果证明中位数的性质正确,则该题就可以用求解中位数来解题):
首先,给定一个从小到大的数列x1,x2,……,xn,设x是从x1到xn与其绝对差之和最小的数,则显然x位于x1与xn之间。那么,由于x1,xn与它们之间的任意一点的距离之和都相等,且都等于xn-x1,因此接下来可以不考虑x1与xn,而考虑剩下的从x2到x[n-1]的数,同样显然有x必然位于x2和x[n-1]之间,依次类推,最后得出的结论是x就是该数列中间的那个数,或者是中间的那两个数之一,而这个数就是中位数。
结论:数列的中位数就是该数列各个数与其绝对差之和最小的数。
Read full article from 邮局选址问题 - Xredman - 博客园

Labels

LeetCode (1432) GeeksforGeeks (1122) LeetCode - Review (1067) Review (882) Algorithm (668) to-do (609) Classic Algorithm (270) Google Interview (237) Classic Interview (222) Dynamic Programming (220) DP (186) Bit Algorithms (145) POJ (141) Math (137) Tree (132) LeetCode - Phone (129) EPI (122) Cracking Coding Interview (119) DFS (115) Difficult Algorithm (115) Lintcode (115) Different Solutions (110) Smart Algorithm (104) Binary Search (96) BFS (91) HackerRank (90) Binary Tree (86) Hard (79) Two Pointers (78) Stack (76) Company-Facebook (75) BST (72) Graph Algorithm (72) Time Complexity (69) Greedy Algorithm (68) Interval (63) Company - Google (62) Geometry Algorithm (61) Interview Corner (61) LeetCode - Extended (61) Union-Find (60) Trie (58) Advanced Data Structure (56) List (56) Priority Queue (53) Codility (52) ComProGuide (50) LeetCode Hard (50) Matrix (50) Bisection (48) Segment Tree (48) Sliding Window (48) USACO (46) Space Optimization (45) Company-Airbnb (41) Greedy (41) Mathematical Algorithm (41) Tree - Post-Order (41) ACM-ICPC (40) Algorithm Interview (40) Data Structure Design (40) Graph (40) Backtracking (39) Data Structure (39) Jobdu (39) Random (39) Codeforces (38) Knapsack (38) LeetCode - DP (38) Recursive Algorithm (38) String Algorithm (38) TopCoder (38) Sort (37) Introduction to Algorithms (36) Pre-Sort (36) Beauty of Programming (35) Must Known (34) Binary Search Tree (33) Follow Up (33) prismoskills (33) Palindrome (32) Permutation (31) Array (30) Google Code Jam (30) HDU (30) Array O(N) (29) Logic Thinking (29) Monotonic Stack (29) Puzzles (29) Code - Detail (27) Company-Zenefits (27) Microsoft 100 - July (27) Queue (27) Binary Indexed Trees (26) TreeMap (26) to-do-must (26) 1point3acres (25) GeeksQuiz (25) Merge Sort (25) Reverse Thinking (25) hihocoder (25) Company - LinkedIn (24) Hash (24) High Frequency (24) Summary (24) Divide and Conquer (23) Proof (23) Game Theory (22) Topological Sort (22) Lintcode - Review (21) Tree - Modification (21) Algorithm Game (20) CareerCup (20) Company - Twitter (20) DFS + Review (20) DP - Relation (20) Brain Teaser (19) DP - Tree (19) Left and Right Array (19) O(N) (19) Sweep Line (19) UVA (19) DP - Bit Masking (18) LeetCode - Thinking (18) KMP (17) LeetCode - TODO (17) Probabilities (17) Simulation (17) String Search (17) Codercareer (16) Company-Uber (16) Iterator (16) Number (16) O(1) Space (16) Shortest Path (16) itint5 (16) DFS+Cache (15) Dijkstra (15) Euclidean GCD (15) Heap (15) LeetCode - Hard (15) Majority (15) Number Theory (15) Rolling Hash (15) Tree Traversal (15) Brute Force (14) Bucket Sort (14) DP - Knapsack (14) DP - Probability (14) Difficult (14) Fast Power Algorithm (14) Pattern (14) Prefix Sum (14) TreeSet (14) Algorithm Videos (13) Amazon Interview (13) Basic Algorithm (13) Codechef (13) Combination (13) Computational Geometry (13) DP - Digit (13) LCA (13) LeetCode - DFS (13) Linked List (13) Long Increasing Sequence(LIS) (13) Math-Divisible (13) Reservoir Sampling (13) mitbbs (13) Algorithm - How To (12) Company - Microsoft (12) DP - Interval (12) DP - Multiple Relation (12) DP - Relation Optimization (12) LeetCode - Classic (12) Level Order Traversal (12) Prime (12) Pruning (12) Reconstruct Tree (12) Thinking (12) X Sum (12) AOJ (11) Bit Mask (11) Company-Snapchat (11) DP - Space Optimization (11) Dequeue (11) Graph DFS (11) MinMax (11) Miscs (11) Princeton (11) Quick Sort (11) Stack - Tree (11) 尺取法 (11) 挑战程序设计竞赛 (11) Coin Change (10) DFS+Backtracking (10) Facebook Hacker Cup (10) Fast Slow Pointers (10) HackerRank Easy (10) Interval Tree (10) Limited Range (10) Matrix - Traverse (10) Monotone Queue (10) SPOJ (10) Starting Point (10) States (10) Stock (10) Theory (10) Tutorialhorizon (10) Kadane - Extended (9) Mathblog (9) Max-Min Flow (9) Maze (9) Median (9) O(32N) (9) Quick Select (9) Stack Overflow (9) System Design (9) Tree - Conversion (9) Use XOR (9) Book Notes (8) Company-Amazon (8) DFS+BFS (8) DP - States (8) Expression (8) Longest Common Subsequence(LCS) (8) One Pass (8) Quadtrees (8) Traversal Once (8) Trie - Suffix (8) 穷竭搜索 (8) Algorithm Problem List (7) All Sub (7) Catalan Number (7) Cycle (7) DP - Cases (7) Facebook Interview (7) Fibonacci Numbers (7) Flood fill (7) Game Nim (7) Graph BFS (7) HackerRank Difficult (7) Hackerearth (7) Inversion (7) Kadane’s Algorithm (7) Manacher (7) Morris Traversal (7) Multiple Data Structures (7) Normalized Key (7) O(XN) (7) Radix Sort (7) Recursion (7) Sampling (7) Suffix Array (7) Tech-Queries (7) Tree - Serialization (7) Tree DP (7) Trie - Bit (7) 蓝桥杯 (7) Algorithm - Brain Teaser (6) BFS - Priority Queue (6) BFS - Unusual (6) Classic Data Structure Impl (6) DP - 2D (6) DP - Monotone Queue (6) DP - Unusual (6) DP-Space Optimization (6) Dutch Flag (6) How To (6) Interviewstreet (6) Knapsack - MultiplePack (6) Local MinMax (6) MST (6) Minimum Spanning Tree (6) Number - Reach (6) Parentheses (6) Pre-Sum (6) Probability (6) Programming Pearls (6) Rabin-Karp (6) Reverse (6) Scan from right (6) Schedule (6) Stream (6) Subset Sum (6) TSP (6) Xpost (6) n00tc0d3r (6) reddit (6) AI (5) Abbreviation (5) Anagram (5) Art Of Programming-July (5) Assumption (5) Bellman Ford (5) Big Data (5) Code - Solid (5) Code Kata (5) Codility-lessons (5) Coding (5) Company - WMware (5) Convex Hull (5) Crazyforcode (5) DFS - Multiple (5) DFS+DP (5) DP - Multi-Dimension (5) DP-Multiple Relation (5) Eulerian Cycle (5) Graph - Unusual (5) Graph Cycle (5) Hash Strategy (5) Immutability (5) Java (5) LogN (5) Manhattan Distance (5) Matrix Chain Multiplication (5) N Queens (5) Pre-Sort: Index (5) Quick Partition (5) Quora (5) Randomized Algorithms (5) Resources (5) Robot (5) SPFA(Shortest Path Faster Algorithm) (5) Shuffle (5) Sieve of Eratosthenes (5) Strongly Connected Components (5) Subarray Sum (5) Sudoku (5) Suffix Tree (5) Swap (5) Threaded (5) Tree - Creation (5) Warshall Floyd (5) Word Search (5) jiuzhang (5)

Popular Posts