Lecture 135: Longest Common Subsequence || DP on Strings

In this Video, we are going to learn about Dynamic Programming. This Video marks the start of India's Biggest DP Series.

There is a lot to learn, Keep in mind “ Mnn bhot karega k chor yrr apne se nahi hoga ya maza nahi aara, Just ask 1 question “ Why I started ? “

Questions Links:

Do provide you feedback in the comments, we are going to make it best collectively.

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Telegram Group Link: Love Babbar CODE HELP

Intro Sequence: We have bought all the required Licenses of the Audio, Video & Animation used.

#DP_Series #LoveBabbar

[praveennemagoudar]

U r genius Bhaiya. Hats off. GOD of DSA.

[manishdv]

Sir apka ye series maine kuch hi din pehle start kiya hai .
You are providing an amazing content which makes it easy for anyone to understand computer programming.
You are doing an amazing job!! Thank you sir!! @LoveBabbar

[vedantraut]

// COMPLETE CODE WITH COMMENTS

class Solution {
public:

int solve(string& a, string& b, int i, int j){

// Base Case
if(i == a.length())
return 0;

if(j == b.length())
return 0;

int ans = 0;

if(a[i] == b[j])
ans = 1 + solve(a, b, i+1, j+1);

else
{
ans = max(solve(a, b, i+1, j), solve(a, b, i, j+1));
}

return ans;
}

int solveMem(string& a, string& b, int i, int j, vector<vector<int>> &dp){

// Base Case
if(i == a.length())
return 0;

if(j == b.length())
return 0;

if(dp[i][j] != -1)
return dp[i][j];

int ans = 0;

if(a[i] == b[j])
ans = 1 + solveMem(a, b, i+1, j+1, dp);

else
{
ans = max(solveMem(a, b, i+1, j, dp), solveMem(a, b, i, j+1, dp));
}

return dp[i][j] = ans;
}

int solveTab(string& a, string& b){

int n1 = a.length();
int n2 = b.length();

vector<vector<int>> dp(n1+1, vector<int> (n2+1, 0));

for(int i = n1-1; i>=0; i--){
for(int j = n2-1; j>=0; j--){
int ans = 0;

if(a[i] == b[j])
ans = 1 + dp[i+1][j+1];

else
{
ans = max(dp[i+1][j], dp[i][j+1]);
}

dp[i][j] = ans;
}
}

return dp[0][0];
}

int solveSpaceOP(string& a, string& b){

int n1 = a.length();
int n2 = b.length();

vector<vector<int>> dp(n1+1, vector<int> (n2+1, 0));

vector<int> currRow(n2+1, 0);
vector<int> nextRow(n2+1, 0);

for(int i = n1-1; i>=0; i--){
for(int j = n2-1; j>=0; j--){
int ans = 0;

if(a[i] == b[j])
ans = 1 + nextRow[j+1];

else
{
ans = max(nextRow[j], currRow[j+1]);
}

currRow[j] = ans;
}

nextRow = currRow;
}

return nextRow[0];
}

int text1, string text2) {
// RECURSION
// return solve(text1, text2, 0, 0);

// RECURSION + MEMOIZATION
/*
int n1 = text1.length();
int n2 = text2.length();

vector<vector<int>> dp(n1+1, vector<int> (n2+1, -1));

return solveMem(text1, text2, 0, 0, dp);
*/

// TABULATION
// return solveTab(text1, text2);

// SPACE OPTIMIZATION
return solveSpaceOP(text1, text2);
}
};

[arvindmali]

Amazing video as always....Thankkk youuuu bhaiya😍

[Vital_Truth]

I really love to learn by you <- Babbar Bhaiya -> 😍❤

[sukhjitsingh]

Thanks Babbar Sir Fire 🔥 back to finish Dp series

[Sambyal-ny]

Appreciate your work. Thank you so much.

[deepakumar]

Sir aapne top down me jo space Kam karne k liye do row liya hai usme aapne bola unki size min(lengths of strings) but ye galat hai aapko max Lena padega

[Kinggaming-hpqp]

really helpful bhaiya this series is very popular in future .

[nothinginsideme]

Very nice explanation sir, thank you so much

[Deepak-umzq]

Thank you bhaiya for such amazing content.☺

[Here.s_how]

I have noticed that some of the tutors use memoization with bottom up and some with top down and vice versa

[BombSquadHindiTipsTricks]

can this ques be solved using 4 variables only?

[GauravHaritas]

Bhaiya #QnA Why didn't you go to foreign country for job purpose or to stay there itself ?