Add code for longest bitonic subsequence

Author: coderick14

LongestBitonicSequence.cpp

@@ -0,0 +1,59 @@
+#include <bits/stdc++.h>
+using namespace std;
+
+void printLIS(vector<int> &a, vector<int> &prev, int pos) {
+    if(pos<0)
+        return;
+    printLIS(a, prev, prev[pos]);
+    cout<<a[pos]<<" ";
+}
+
+void printLDS(vector<int> &a, vector<int> &next, int pos, int n) {
+    if(pos>=n)
+        return;
+    cout<<a[pos]<<" ";
+    printLDS(a, next, next[pos],n);
+}
+
+int main() {
+    int i,j,n,pos;
+    cin>>n;
+    vector<int> a(n), LIS(n), LDS(n);
+    vector<int> prev(n,-1), next(n,n);
+    for(i=0; i<n; i++) {
+        cin>>a[i];
+        LIS[i] = LDS[i] = 1;
+    }
+
+    for(i=1; i<n; i++) {
+        for(j=0; j<i; j++) {
+            if(a[j]<a[i] && LIS[i]<LIS[j]+1) {
+                LIS[i] = LIS[j] + 1;
+                prev[i] = j;
+            }
+        }
+    }
+
+    for(i=n-2; i>=0; i--) {
+        for(j=n-1; j>i; j--) {
+            if(a[i]>a[j] && LDS[i]<LDS[j]+1) {
+                LDS[i] = LDS[j] + 1;
+                next[i] = j;
+            }
+        }
+    }
+
+    int maxim = LIS[0] + LDS[0] - 1;
+    pos = 0;
+    for(i=1; i<n; i++) {
+        if(LIS[i] + LDS[i] - 1 > maxim) {
+            maxim = LIS[i] + LDS[i] - 1;
+            pos = i;
+        }
+    }
+    cout<<maxim<<"\n";
+    printLIS(a,prev,pos);
+    printLDS(a,next,next[pos],n);
+    cout<<endl;
+    return 0;
+}