Created
January 8, 2018 01:02
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binary search - pair with difference
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using System; | |
using System.Collections.Generic; | |
class Solution | |
{ | |
public static int[,] FindPairsWithGivenDifference(int[] arr, int k) // [0, -1, -2, 2, 1], k = 1 | |
{ | |
if(arr == null || arr.Length == 0 || k < 0) // false | |
{ | |
return new int[0,0]; | |
} | |
int length = arr.Length; // 5 | |
Array.Sort(arr); // -2, -1, 0, 1, 2 | |
var pair = new List<int[]>(); | |
for(int i = 0; i < length - 1; i++) // 0, 1, 2, 3, | |
{ | |
var current = arr[i]; // 0 | |
var search = current + k; // 1 | |
if(binarySearch(arr, i + 1, length - 1, search)) // 1, 4, 1 | |
{ | |
pair.Add(new int[]{search, current}); // (1, 0) | |
} | |
} | |
// convert to the two dimension array | |
var pairLength = pair.Count; | |
var pairArray = new int[pairLength, 2]; | |
for(int i = 0; i < pairLength; i++) | |
{ | |
pairArray[i, 0] = pair[i][0]; | |
pairArray[i, 1] = pair[i][1]; | |
} | |
return pairArray; | |
} | |
private static bool binarySearch(int[] numbers, int start, int end, int search ) // 1, 4, 1 | |
{ | |
while(start <= end) // true | |
{ | |
int middle = start + (end - start)/ 2; // 2 | |
var middleValue = numbers[middle]; // 0 | |
var found = middleValue == search; // false | |
if(found) | |
{ | |
return true; | |
} | |
else if(middleValue < search) // 0 < 1 | |
{ | |
start = middle + 1; // 3 | |
} | |
else | |
{ | |
end = middle - 1; | |
} | |
} | |
return false; | |
} | |
static void Main(string[] args) | |
{ | |
var pair = FindPairsWithGivenDifference(new int[]{0, -1, -2, 2, 1}, 1); | |
var rows = pair.GetLength(0); | |
for(int i = 0; i < rows; i++) | |
{ | |
Console.WriteLine(pair[i, 0] + "," + pair[i, 1]); | |
} | |
} | |
} | |
/* | |
[0, -1, -2, 2, 1], k = 1 x - y = k , k = 1, x > y | |
O(n^2) | |
sort the array - O(nlogn) | |
[-2, -1, 0, 1, 2] -> all possible pairs -2, need to find -2 + 1 = -1, binary search nlogn | |
O(nlogn) | |
extra space | |
scan the array, in the same time, put past integer in hashset, | |
-2, try to find -3, -2 hashset | |
-1, -2 in hashset, [-1, -2] result list, | |
[-1] in hashset | |
-> O(n), space O(n) | |
*/ |
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