Dynamic Programming - Part II
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The document is a lecture on dynamic programming, focusing on various algorithms such as maximum value contiguous subarray, longest increasing subsequence, and coin change. It details algorithmic approaches, including brute force, greedy variations, and dynamic programming solutions with time complexities. Additionally, it includes sample runs and insights on optimal substructure in dynamic programming.
![MaxValue = - infinity
for i = 1 to n {
for j = i to n {
currSum = findSubArraySum(i,j)
if CurrSum > MaxValue, then MaxValue = CurrSum
}
}
Procedure FindSubArraySum(i,j)
Double sum = 0
For int k = i to j {
sum = sum + A[k]
}
return sum
}
Algorithms Dynamic Programming - Part II 6
ALGORITHM MVCS1
Brute Force
Search!
O(n3) time](https://image.slidesharecdn.com/l7dp2-141006202036-conversion-gate02/85/Dynamic-Programming-Part-II-6-320.jpg)
![Procedure InitSubArraySums() {
for int i = 1 to n {
double sum = 0
for int k = i to n {
sum = sum + A(k)
SubArraySum[i][k] = sum
}
}
}
InitSubArraySums();
MaxValue = - infinity
for i = 1 to n {
for j = i to n {
currSum = SubArraySum[i][j]
If currSum > MaxValue, then MaxValue = currSum
}
}
Algorithms Dynamic Programming - Part II 7
ALGORITHM MVCS2
Still a full search,
but don’t
recompute sums
O(n2) time](https://image.slidesharecdn.com/l7dp2-141006202036-conversion-gate02/85/Dynamic-Programming-Part-II-7-320.jpg)
![Using Dynamic Programming Template
1. N: MVCS(i): value of MVCS ending at position i.
2. O: Prove Optimal Substructure Holds (What is our
claim?)
3. R: MVCS(i) = max {MVCS(i-1) + A[i],A[i]}
4. A: Start from left, and keep track of maximum
MVCS(i) encountered.
1. For I = 1 to n
Algorithms Dynamic Programming - Part II 9
MVCS3
O(n) time](https://image.slidesharecdn.com/l7dp2-141006202036-conversion-gate02/85/Dynamic-Programming-Part-II-9-320.jpg)
![ Using the Array used in class
A[]: 22, -17, -71, 12, -22, 81, -10, 63
MVCS[]: 22, 5, -66, 12, -10, 81, 71, 134
Algorithms Dynamic Programming - Part II 10
SAMPLE RUN OF MVCS3](https://image.slidesharecdn.com/l7dp2-141006202036-conversion-gate02/85/Dynamic-Programming-Part-II-10-320.jpg)
![ Given array A(1..n)
LIS(i) = longest strictly increasing subsequence that
ends at i.
LIS(i) = max {LIS(j)} + 1, such that j < i, and A[j] <
A[i]
[Or A[j] ≤ A[i] if we are looking for that condition]
Algorithms Dynamic Programming - Part II 12
LONGEST INCREASING SUBSEQUENCE](https://image.slidesharecdn.com/l7dp2-141006202036-conversion-gate02/85/Dynamic-Programming-Part-II-12-320.jpg)
Dynamic Programming - Part II
- 1. Design and Analysis of Algorithms DYNAMIC PROGRAMMING PART II Maximum Value Contiguous Subarray Maximum Increasing Subsequence Coin Change Algorithms Dynamic Programming - Part II 1
- 2. Instructor Prof. Amrinder Arora [email protected] Please copy TA on emails Please feel free to call as well Available for study sessions Science and Engineering Hall GWU Algorithms Dynamic Programming - Part II 2 LOGISTICS
- 3. Algorithms Analysis Asymptotic NP- Completeness Design D&C Greedy DP Graph B&B Applications Algorithms Dynamic Programming - Part II 3 WHERE WE ARE Done Done Finishing today.. Done
- 4. http://video.google.com/videoplay?docid=16073867 32227802988# http://people.csail.mit.edu/bdean/6.046/dp/ Algorithms Dynamic Programming - Part II 4 DP (CONT.)
- 5. Given an Array A(1..n) To find A(i..j) such that the sum of the terms in the subarray is maximized. Insights If no negative terms in the array, then of course, we just select the entire array. So, this problem is meaningful only when we have negative numbers We can find sum of all contiguous subarrays in O(n3) time. Can we do better? Algorithms Dynamic Programming - Part II 5 MAXIMUM VALUE CONTIGUOUS SUBSEQUENCE
- 6. MaxValue = - infinity for i = 1 to n { for j = i to n { currSum = findSubArraySum(i,j) if CurrSum > MaxValue, then MaxValue = CurrSum } } Procedure FindSubArraySum(i,j) Double sum = 0 For int k = i to j { sum = sum + A[k] } return sum } Algorithms Dynamic Programming - Part II 6 ALGORITHM MVCS1 Brute Force Search! O(n3) time
- 7. Procedure InitSubArraySums() { for int i = 1 to n { double sum = 0 for int k = i to n { sum = sum + A(k) SubArraySum[i][k] = sum } } } InitSubArraySums(); MaxValue = - infinity for i = 1 to n { for j = i to n { currSum = SubArraySum[i][j] If currSum > MaxValue, then MaxValue = currSum } } Algorithms Dynamic Programming - Part II 7 ALGORITHM MVCS2 Still a full search, but don’t recompute sums O(n2) time
- 8. What can be a greedy variation of MVCS algorithm? What can be a D&C version of MVCS algorithm? How about Dynamic Programming? Algorithms Dynamic Programming - Part II 8 USING OTHER TECHNIQUES FOR MVCS
- 9. Using Dynamic Programming Template 1. N: MVCS(i): value of MVCS ending at position i. 2. O: Prove Optimal Substructure Holds (What is our claim?) 3. R: MVCS(i) = max {MVCS(i-1) + A[i],A[i]} 4. A: Start from left, and keep track of maximum MVCS(i) encountered. 1. For I = 1 to n Algorithms Dynamic Programming - Part II 9 MVCS3 O(n) time
- 10. Using the Array used in class A[]: 22, -17, -71, 12, -22, 81, -10, 63 MVCS[]: 22, 5, -66, 12, -10, 81, 71, 134 Algorithms Dynamic Programming - Part II 10 SAMPLE RUN OF MVCS3
- 11. Given array A(1..n) Find a subsequence (not necessarily contiguous) that is strictly increasing. For example {1, 7, 2, 8, 4, 1, 6, 11, 3, 15, 5, 12, 14} Algorithms Dynamic Programming - Part II 11 LONGEST INCREASING SUBSEQUENCE Longest subsequence is of length 7: {1, .., 2, .., 4, .., 6, 11, .., .., .., 12, 14}
- 12. Given array A(1..n) LIS(i) = longest strictly increasing subsequence that ends at i. LIS(i) = max {LIS(j)} + 1, such that j < i, and A[j] < A[i] [Or A[j] ≤ A[i] if we are looking for that condition] Algorithms Dynamic Programming - Part II 12 LONGEST INCREASING SUBSEQUENCE
- 13. What is the time complexity of this algorithm? Algorithms Dynamic Programming - Part II 13 LIS
- 14. Using the Array used in Class {1, 7, 2, 8, 4, 1, 6, 11, 3, 15, 5, 12, 14} {1, 2, 2, 3, 3, 1, 4, 5, 3, 6, 4, 6, 7} What are the LIS values? Algorithms Dynamic Programming - Part II 14 SAMPLE RUN OF LIS
- 15. Given a set of coins with values v1, v2, … vn such that v1 = 1, v1 < v2 < v3 < v4 < … < vn We want to make change for a given value S using as few coins as possible Algorithms Dynamic Programming - Part II 15 COIN CHANGE
- 16. http://people.csail.mit.edu/bdean/6.046/dp/ Algorithms Dynamic Programming - Part II 16 AN INTERESTING SET OF PROBLEMS
- 17. Algorithms Dynamic Programming - Part II 17 80% OF SUCCESS IS SHOWING UP.
- 18. Algorithms Dynamic Programming - Part II 18 REST 80% OF SUCCESS IS BEING PRESENT!
- 19. CS 6212 Analysis Asymptotic NP- Completeness Design D&C Greedy DP Graph B&B Applications Algorithms Dynamic Programming - Part II 19 WHERE WE ARE Done Done Done Done