CC150 - 11.6

Question:

Given an M x N matrix in which each row and each column is sorted in ascending order, write a method to find an element.

 

 1 package POJ;
 2 
 3 public class Main {
 4 
 5     /**
 6      * 
 7      * 11.6 Given an M x N matrix in which each row and each column is sorted in
 8      * ascending order, write a method to find an element.
 9      * 
10      */
11     public static void main(String[] args) {
12         Main so = new Main();
13     }
14 
15     public static Coordinate findElement(int[][] matrix, int x) {
16         Coordinate origin = new Coordinate(0, 0);
17         Coordinate dest = new Coordinate(matrix.length - 1,
18                 matrix[0].length - 1);
19         return findElement(matrix, origin, dest, x);
20     }
21 
22     public static Coordinate findElement(int[][] matrix, Coordinate origin,
23             Coordinate dest, int x) {
24         if (!origin.inbounds(matrix) || !dest.inbounds(matrix)) {
25             return null;
26         }
27         if (matrix[origin.row][origin.column] == x)
28             return origin;
29         if (!origin.isBefore(dest))
30             return null;
31         Coordinate start = (Coordinate) origin.clone();
32         int diagDist = Math.min(dest.row - origin.row, dest.column
33                 - origin.column);
34         Coordinate end = new Coordinate(start.row + diagDist, start.column
35                 + diagDist);
36         Coordinate p = new Coordinate(0, 0);
37 
38         while (start.isBefore(end)) {
39             p.setToAverage(start, end);
40             if (x > matrix[p.row][p.column]) {
41                 start.row = p.row + 1;
42                 start.column = p.column + 1;
43             } else {
44                 end.row = p.row - 1;
45                 end.column = p.column - 1;
46             }
47         }
48         return partitionAndSearch(matrix, origin, dest, start, x);
49     }
50 
51     private static Coordinate partitionAndSearch(int[][] matrix,
52             Coordinate origin, Coordinate dest, Coordinate pivot, int elem) {
53         // TODO Auto-generated method stub
54         Coordinate lowerLeftOrigin = new Coordinate(pivot.row, origin.column);
55         Coordinate lowerLeftDest = new Coordinate(dest.row, pivot.column - 1);
56         Coordinate upperRightOrigin = new Coordinate(origin.row, pivot.column);
57         Coordinate upperRightDest = new Coordinate(pivot.row - 1, dest.column);
58         Coordinate lowerLeft = findElement(matrix, lowerLeftOrigin,
59                 lowerLeftDest, elem);
60         if (lowerLeft == null)
61             return findElement(matrix, upperRightOrigin, upperRightDest, elem);
62         return lowerLeft;
63     }
64 }
65 
66 class Coordinate implements Cloneable {
67     int row;
68     int column;
69 
70     public Coordinate(int r, int c) {
71         row = r;
72         column = c;
73     }
74 
75     public boolean inbounds(int[][] matrix) {
76         return row >= 0 && column >= 0 && row < matrix.length
77                 && column < matrix[0].length;
78     }
79 
80     public boolean isBefore(Coordinate p) {
81         return row <= p.row && column <= p.column;
82     }
83 
84     public Object clone() {
85         return new Coordinate(row, column);
86     }
87 
88     public void setToAverage(Coordinate min, Coordinate max) {
89         row = (min.row + max.row) / 2;
90         column = (min.column + max.column) / 2;
91     }
92 }

 

posted @ 2014-09-01 01:51  Phoebe815  阅读(234)  评论(0)  编辑  收藏  举报