zoukankan      html  css  js  c++  java
  • Leetcode: Kth Smallest Element in a Sorted Matrix

    Given a n x n matrix where each of the rows and columns are sorted in ascending order, find the kth smallest element in the matrix.
    
    Note that it is the kth smallest element in the sorted order, not the kth distinct element.
    
    Example:
    
    matrix = [
       [ 1,  5,  9],
       [10, 11, 13],
       [12, 13, 15]
    ],
    k = 8,
    
    return 13.
    Note: 
    You may assume k is always valid, 1 ≤ k ≤ n2.

    Heap: you need to know the row number and column number of that element(so we can create a tuple class here)

     1 public class Solution {
     2     public int kthSmallest(int[][] matrix, int k) {
     3         Comparator<Tuple> comp = new Comparator<Tuple>() {
     4             public int compare(Tuple tp1, Tuple tp2) {
     5                 return tp1.val - tp2.val;
     6             }
     7         };
     8         
     9         PriorityQueue<Tuple> minHeap = new PriorityQueue<Tuple>(matrix.length, comp);
    10         
    11         int res = 0;
    12         
    13         for (int row=0; row<matrix.length; row++) {
    14             minHeap.offer(new Tuple(row, 0, matrix[row][0]));
    15         }
    16         
    17         
    18         for (int i=1; i<=k; i++) {
    19             Tuple tp = minHeap.poll();
    20             if (i == k) {
    21                 res = tp.val;
    22                 break;
    23             }
    24             if (tp.y < matrix.length-1) minHeap.offer(new Tuple(tp.x, tp.y+1, matrix[tp.x][tp.y+1]));
    25         }
    26         return res;
    27     }
    28     
    29     public class Tuple {
    30             int x;
    31             int y;
    32             int val;
    33             public Tuple(int i, int j, int value) {
    34                 this.x = i;
    35                 this.y = j;
    36                 this.val = value;
    37             }
    38     }
    39 }

    Binary Search方法:(12/28仔细看了之后觉得没必要深究,有时间再去深究吧)

     1 public class Solution {
     2     public int kthSmallest(int[][] matrix, int k) {
     3         int lo = matrix[0][0], hi = matrix[matrix.length - 1][matrix[0].length - 1] + 1;//[lo, hi)
     4         while(lo < hi) {
     5             int mid = lo + (hi - lo) / 2;
     6             int count = 0,  j = matrix[0].length - 1;
     7             for(int i = 0; i < matrix.length; i++) {
     8                 while(j >= 0 && matrix[i][j] > mid) j--;
     9                 count += (j + 1);
    10             }
    11             if(count < k) lo = mid + 1;
    12             else hi = mid;
    13         }
    14         return lo;
    15     }
    16 }

    referred to https://discuss.leetcode.com/topic/52948/share-my-thoughts-and-clean-java-code/2

  • 相关阅读:
    2016去哪儿编程题:乘坐公交
    lintcode:交错正负数
    lintcode:Ugly Number I
    KMP算法
    适配器模式
    迭代器模式
    命令模式
    外观模式
    工厂方法模式
    代理模式
  • 原文地址:https://www.cnblogs.com/EdwardLiu/p/6109080.html
Copyright © 2011-2022 走看看