Two Pointer and BS ques

Author: prajwal714

Interview Bit/Binary Search/Allocate Books.cpp

@@ -0,0 +1,51 @@
+bool isValid(vector<int> A, int maxStud, int mid)
+{
+    int i;
+    int students=1;
+    long long int sum=0;
+    for(i=0;i<A.size();i++)
+    {
+        sum+=A[i];
+        if(sum>mid)
+        {
+            students++;
+            sum=A[i];
+        }
+        
+        if(students>maxStud)
+        return false;
+    }
+    
+    return true;
+}
+
+int Solution::books(vector<int> &A, int B) {
+    
+    if(B>A.size())
+    return -1;
+    
+    int start=INT_MIN;
+    long long int end=0, res;
+    int i;
+    for(i=0;i<A.size();i++)
+    {
+        start=max(start,A[i]);
+        end+=A[i];
+    }
+    
+    while(start<=end)
+    {
+        long long int mid=start+(end-start)/2;
+        
+        if(isValid(A,B,mid)==true)
+        {
+        res=mid;            
+        end=mid-1;
+        }
+        else
+        start=mid+1;
+    }
+    
+    return res;
+}
+

Interview Bit/Binary Search/Merge Two Sorted Lists II.cpp

@@ -0,0 +1,96 @@
+int findPivot(vector<int> arr, int low, int high)
+{
+    if(low>high)
+    return -1;
+    
+    int mid=(high+low)/2;
+   
+   if(mid<high && arr[mid]>arr[mid+1])
+   return mid;
+   
+   if(mid>low&&arr[mid]<arr[mid-1])
+   return mid-1;
+   
+   if(arr[low]>arr[mid])
+   return findPivot(arr,low,mid-1);
+  
+   return findPivot(arr,mid+1,high);
+}
+int binSearch(vector<int> arr, int low, int high, int key)
+{
+    if(low>high)
+    return -1;
+    
+    int mid=(high+low)/2;
+    
+    if(arr[mid]==key)
+    return mid;
+    
+    else if(arr[mid]<key)
+    binSearch(arr,mid+1,high,key);
+    
+    else
+    binSearch(arr,low,mid-1,key);
+}
+
+int Solution::search(const vector<int> &A, int B) {
+    
+   int min=0,max=0;
+
+for(int i=1;i<A.size();i++)
+{
+    if(A[i]>=A[max])
+    {
+        max=i;
+    }
+    else
+    {
+        break;
+    }
+}
+
+if(B<A[min])
+{
+    min=max+1;
+    max=A.size()-1;
+}
+
+while(min<=max)
+{
+    int mid=(min+max)/2;
+    
+    if(A[mid]==B)
+    {
+        return mid;
+    }
+    
+    if(A[mid]>B)
+    {
+        max=mid-1;
+    }
+    else
+    {
+        min=mid+1;
+    }
+}
+
+return -1;
+    
+}
+========================================================================================================
+int Solution::search(const vector<int> &A, int B) {
+    int n = A.size();
+    int low = 0, high = n-1;
+    while(low<=high){
+        int mid = low + (high-low)/2;
+        if(A[mid] == B) return mid;
+        else if(A[0]<=A[mid]){//i.e. left part is sorted
+            if(A[0]<=B && B < A[mid]) high = mid-1;//B lies on left part
+            else low = mid+1;
+        }else{//right part is sorted
+            if(A[mid] < B && B<=A[n-1]) low = mid+1;//B lies on right part
+            else high = mid-1;
+        }
+    }
+    return -1;
+}

Interview Bit/Binary Search/Rotated sorted array.cpp

@@ -0,0 +1,31 @@
+int Solution::threeSumClosest(vector<int> &A, int B) {
+    
+    int i,curr,start,end;
+    int sum=0, res=INT_MAX, ans;
+    sort(A.begin(), A.end());
+    for(i=A.size()-1;i>=2;i--)
+    {
+        curr=A[i];
+        start=0; end=i-1;
+        while(start<end)
+        {
+            sum=A[start]+A[end]+curr;
+            
+            if(abs(sum-B)<res)
+            {
+                res=abs(sum-B);
+                ans=sum;
+            }
+            
+            if(sum<B)
+            start++;
+            else if(sum>B)
+            end--;
+            else
+            return sum;
+        }
+    }
+    return ans;
+    
+}
+

Interview Bit/Two Pointers/3 sum.cpp

@@ -0,0 +1,29 @@
+int Solution::maxArea(vector<int> &A) {
+    long long int res=0;
+    long long int sum=0;
+    
+    int start=0,end=A.size()-1;
+    
+    while(start<end)
+    {
+        sum=(end-start)*min(A[start],A[end]);
+        
+        if(sum>res)
+        res=sum;
+        if(A[start]<A[end])
+        {
+            start++;
+        }
+        else if(A[start]>=A[end])
+        {
+            end--;
+        }
+       
+    }
+    
+    return res;
+}
+
+=========================================================================
+
+

Interview Bit/Two Pointers/Container with most water.cpp

@@ -0,0 +1,13 @@
+void Solution::merge(vector<int> &A, vector<int> &B) {
+    // Do not write main() function.
+    // Do not read input, instead use the arguments to the function.
+    // Do not print the output, instead return values as specified
+    // Still have a doubt. Checkout www.interviewbit.com/pages/sample_codes/ for more details
+   int i = A.size() - 1, j = B.size() - 1, index = A.size() + B.size() - 1;
+    A.resize(A.size() + B.size());
+    while(i >= 0 and j >= 0)
+        A[index--] = (A[i] > B[j]) ? A[i--] : B[j--];
+    while(j >= 0)
+        A[index--] = B[j--];
+}
+