Added Dutch Flag algo (#93)

arrays/README.md

@@ -5,6 +5,7 @@
 1. [Counting Inversions](c-or-cpp/count-inversions.cpp)
 2. [Dutch Flag Algo](c-or-cpp/dutch-flag-algo.cpp)
 3. [Left Rotation of Array](c-or-cpp/left-rotation.cpp)
+4. [Shift Negatives in Array](c-or-cpp/shift-negatives.cpp)
 
 ### Python
 
@@ -17,3 +18,4 @@
 ### Java
 
 1. [Counting Inversions](java/count-inversions.java)
+

arrays/c-or-cpp/shift-negatives.cpp

@@ -0,0 +1,52 @@
+#include<bits/stdc++.h>
+using namespace std;
+
+// Move all negative elements to left and positives to right side of the array
+
+// Approach 1 --> Partition Algo - O(n)
+void shiftNegatives_A(int arr[],int size){
+    int j = -1,pivot=0;
+    for(int i=0;i<size;++i){
+        if(arr[i]<pivot){
+            j++;
+            swap(arr[i],arr[j]);
+        }
+    }
+}
+
+// Approach 2 -->  Two-pointer Method - O(n)
+void shiftNegatives_B(int arr[],int size){
+    int left = 0, right =  size-1;
+    while(left < right){
+        if(arr[left]<0 && arr[right]<0){
+            left++;
+        }
+        else if(arr[left]>0 && arr[right]>0){
+            right--;
+        }
+        else if(arr[left]>0 && arr[right]<0){
+            swap(arr[left],arr[right]);
+            left++; right--;
+        }
+        else{
+            left++; right--;
+        }
+    }
+}
+
+void printArray(int arr[],int size){
+    for(int i=0;i<size;++i){
+        cout<<arr[i]<<" ";
+    }
+    cout<<endl;
+}
+
+int main()
+{
+    int arr[] = { -1, 2, -3, 4, 5, 6, -7, 8, 9 };
+    int n = sizeof(arr) / sizeof(arr[0]);
+    // shiftNegatives_A(arr, n);
+    // shiftNegatives_B(arr, n);
+    printArray(arr, n);
+    return 0;
+}