Two pointers

Arrays/Q1.java → Java/Arrays/Q1.java

@@ -13,7 +13,7 @@ public static void main(String[] args) {
         }
         int maxEle=arr[0];
         int minEle=arr[0];
-        for(int i=01;i<arr.length;i++){
+        for(int i=1;i<arr.length;i++){
             if(arr[i]>maxEle){
                 maxEle=arr[i];
             }

Sliding window/StringPermutation.py → Patterns/Sliding window/StringPermutation.py

@@ -1,5 +1,9 @@
+#String Permutation using Sliding Window
+#Given two strings s1 and s2, return true if s2 contains a 
+#permutation of s1, or false otherwise.
+#eg: s1 = "abc", s2 = "cbabcabcadef" -> true, because s2 contains "cba", "bac", "abc" which are permutations of s1.
 s1 = "abc"
-s2 = "cbabcabcadef"
+s2 = "cbaccabcadef"
 windowSize = len(s1)
 s1Count = [0] * 26
 s2Count = [0] * 26
@@ -15,4 +19,4 @@
     s2Count[ord(s2[i]) - ord('a')] += 1
     s2Count[ord(s2[i - windowSize]) - ord('a')] -= 1
     if s1Count == s2Count:
-        print("Permutation exist: ",s2[i - windowSize + 1 : i + 1])
+        print("Permutation exist: ",s2[i - windowSize + 1 : i + 1])

Patterns/Two Pointer/DutchFlag.py

@@ -0,0 +1,18 @@
+#Sort the array in increasing order.(use in place array)
+#only numbers allowed in the array : [0,1,2]
+arr = [2,0,2,1,1,0]
+n = len(arr)
+l = 0
+m = 0
+r = len(arr) - 1
+while m <= r:
+    if arr[m] == 0:
+        arr[l],arr[m] = arr[m],arr[l]
+        l += 1
+        m += 1
+    elif arr[m] == 1:
+        m += 1
+    else:
+        arr[m],arr[r] = arr[r],arr[m]
+        r -= 1 
+print(arr)

Patterns/Two Pointer/TwoSum.py

@@ -0,0 +1,13 @@
+#Given an array and target, return 1-based indices pair whose sum = target. only one such pair exists
+numbers = [1, 2, 4, 7, 11, 15]
+target = 15
+l = 0
+r = len(numbers) - 1
+while l < r:
+    if numbers[l] + numbers[r] == target:
+        print([l+1,r+1])
+        break
+    elif numbers[l] + numbers[r] < target:
+        l += 1
+    else:
+        r -= 1

Patterns/Two Pointer/squareArray.py

@@ -0,0 +1,15 @@
+#A non decreasing array is given, return a non decreasing array of their sqaures
+arr = [-4,-1,0,3,10]
+l = 0
+r = len(arr) - 1
+res = [0] * len(arr)
+pos = len(arr) - 1
+while l <= r:
+    if abs(arr[l]) >= abs(arr[r]):
+        res[pos] = arr[l] ** 2
+        l += 1
+    else:
+        res[pos] = arr[r] ** 2
+        r -= 1
+    pos -= 1
+print(res)