Arjun Suresh (talk | contribs) |
Arjun Suresh (talk | contribs) |
||
(18 intermediate revisions by the same user not shown) | |||
Line 18: | Line 18: | ||
==={{Template:Author|Arjun Suresh|{{arjunweb}} }}=== | ==={{Template:Author|Arjun Suresh|{{arjunweb}} }}=== | ||
+ | A key to the solution is that we can continue pressing CTRL-V multiple times and the characters in the buffer will get printed continuously. The recurrence relation for the solution is | ||
+ | |||
+ | sol[n] = max(2 * sol[n-3], 3 * sol[n-4], 4 * sol[n-5]) | n > 6 | ||
+ | and | ||
+ | 1 for 1<= n <= 6 | ||
+ | |||
+ | The recurrence relation is drawn from the fact that, the optimal solution at position $n$ will be obtained by CTRL-A, CTRL-C, CTRL-V sequence starting at either $(n-3)^{th}$ position or $(n-4)^{th}$ position or $(n-5)^{th}$ position. We needn't consider solution at position $(n-6)$ because that is already considered while calculating the solution at position $(n-3)$ which we are considering. Each CTRL-V prints the same number of characters as was on the screen during which the previous CTRL-A was typed. So, if we take $sol[n-3]$, that would mean CTRL-A starting at $n-2$, CTRL-C at $n-1$ and CTRL-V at $n$. So, $sol[n-3]$ is doubled at $n$. If we take $sol[n-4]$, there will be CTRL-V at positions $n-1$ and $n$, and so $sol[n]$ becomes $3$ times $sol[n-4]$. Similarly, if we take $sol[n-5]$, there will be 3 CTRL-V at $n-2$, $n-1$ and $n$ and $sol[n]$ becomes 4 times $sol[n-5]$. | ||
<syntaxhighlight lang="c" name="printa"> | <syntaxhighlight lang="c" name="printa"> | ||
#include <stdio.h> | #include <stdio.h> | ||
− | + | ||
+ | //Returns max of a,b,c | ||
+ | int max(int a, int b, int c) | ||
+ | { | ||
+ | return a > b ? a > c? a:c : b > c? b:c; | ||
+ | } | ||
+ | |||
+ | //Returns 1 if a = max(a,b,c), 2 if b = max(a,b,c) and 3 if c = max(a,b,c) | ||
+ | int maxp(int a, int b, int c) | ||
+ | { | ||
+ | return a > b ? a > c? 1:3 : b > c? 2:3; | ||
+ | } | ||
+ | |||
+ | void print(int *, int); | ||
int main() | int main() | ||
{ | { | ||
− | + | unsigned int n, i; | |
− | + | unsigned long long sol[1000]; | |
− | + | unsigned int prin[1000]; | |
− | + | printf("Enter N: "); | |
− | + | scanf("%u", &n); | |
− | + | ||
− | + | for(i = 1 ;n>5? i<=5: i<= n; i++) | |
− | + | { | |
− | + | sol[i] = i; | |
− | + | prin[i] = 0; | |
− | + | } | |
− | + | if(n >= 6) | |
− | + | { | |
− | + | sol[6] = 6; | |
− | + | prin[6] = 1; | |
− | + | } | |
− | + | for(i = 7; i <= n; i++) | |
− | + | { | |
− | + | sol[i] = max(2 * sol[i-3], 3 * sol[i-4], 4 * sol[i-5]); | |
− | + | prin[i] = maxp(2 * sol[i-3], 3 * sol[i-4], 4 * sol[i-5]); | |
− | + | } | |
− | + | printf("M = %llu\n", sol[n]); | |
− | + | printf("Enter any char to start printing the key sequence: \n"); | |
− | + | scanf("%d", &n); | |
− | + | printf("Printing the sequence: \n\n"); | |
− | + | print(prin, n); | |
− | + | } | |
− | + | ||
− | + | void print(int * prin, int n) | |
− | + | { | |
− | + | if(n < 1) | |
− | + | return; | |
− | + | switch(prin[n]) | |
− | + | { | |
− | + | case 0: | |
− | + | print(prin, n-1); | |
− | + | printf("A\n"); | |
− | + | break; | |
− | + | case 1: | |
− | + | print(prin, n-3); | |
− | + | printf("CTRL-A\nCTRL-C\nCTRL-V\n"); | |
− | + | break; | |
− | + | case 2: | |
− | + | print(prin, n-4); | |
− | + | printf("CTRL-A\nCTRL-C\nCTRL-V\nCTRL-V\n"); | |
− | + | break; | |
− | + | case 3: | |
− | + | print(prin, n-5); | |
− | + | printf("CTRL-A\nCTRL-C\nCTRL-V\nCTRL-V\n"); | |
− | + | } | |
− | + | } | |
− | + | ||
− | + | </syntaxhighlight> | |
− | + | ||
− | + | ===Alternate Solution=== | |
− | + | ||
− | + | The above solution assumes that after CTRL-C, we can do a mouse click as otherwise CTRL-V will override whatever was selected on the screen. If mouse click is not allowed, recurrence relation should be modified as: | |
− | + | ||
− | + | sol[n] = max(2 * sol[n-4], 3 * sol[n-5], 4 * sol[n-6], 5 * sol[n-7]) | n > 7 | |
− | + | and | |
− | + | 1 for 1<= n <= 7 | |
− | + | ||
− | + | The code for this will be: | |
− | + | <syntaxhighlight lang="c" name="printa2"> | |
− | + | #include <stdio.h> | |
− | + | ||
− | + | //Returns max of a,b,c,d | |
− | + | int max(int a, int b, int c, int d) | |
− | + | { | |
− | + | return a > b ? a > c? a > d ? a : d : c > d? c : d : b > c? b > d? b : d : c > d? c : d ; | |
− | + | } | |
− | + | ||
− | + | ||
− | + | //Returns 1 if a = max(a,b,c,d), 2 if b = max(a,b,c,d), 3 if c = max(a,b,c,d) and 4 if d = max(a,b,c,d) | |
− | + | int maxp(int a, int b, int c, int d) | |
− | + | { | |
− | + | return a > b ? a > c? a > d ? 1 : 4 : c > d? 3 : 4 : b > c? b > d? 2 : 4 : c > d? 3 : 4; | |
− | + | } | |
− | + | ||
− | + | void print(int *, int); | |
− | + | ||
− | + | int main() | |
− | + | { | |
− | + | unsigned int n, i; | |
− | + | unsigned long long sol[1000]; | |
− | + | unsigned int prin[1000]; | |
− | + | printf("Enter N: "); | |
− | + | scanf("%u", &n); | |
− | + | ||
− | + | for(i = 1 ;n>7? i<=7: i<= n; i++) | |
− | + | { | |
− | + | sol[i] = i; | |
− | + | prin[i] = 0; | |
− | + | } | |
− | + | ||
− | + | for(i = 8; i <= n; i++) | |
− | + | { | |
− | + | sol[i] = max( 2 * sol[i-4], 3 * sol[i-5], 4 * sol [i-6], 5 * sol[i-7]); | |
− | + | prin[i] = maxp( 2 * sol[i-4], 3 * sol[i-5], 4 * sol [i-6], 5 * sol[i-7]); | |
− | + | } | |
− | + | printf("M = %llu\n", sol[n]); | |
− | + | printf("Enter any char to start printing the key sequence: \n"); | |
− | + | scanf("%d", &n); | |
− | + | printf("Printing the sequence: \n\n"); | |
− | + | print(prin, n); | |
− | + | } | |
− | + | ||
− | + | void print(int * prin, int n) | |
− | + | { | |
− | + | if(n < 1) | |
− | + | return; | |
− | + | switch(prin[n]) | |
− | + | { | |
− | + | case 0: | |
− | + | print(prin, n-1); | |
− | + | printf("A\n"); | |
− | + | break; | |
− | + | case 1: | |
− | + | print(prin, n-4); | |
− | + | printf("CTRL-A\nCTRL-C\nCTRL-V\nCTRL-V\n"); | |
− | + | break; | |
− | + | case 2: | |
− | + | print(prin, n-5); | |
− | + | printf("CTRL-A\nCTRL-C\nCTRL-V\nCTRL-V\nCTRL-V\n"); | |
− | + | break; | |
− | + | case 3: | |
− | + | print(prin, n-6); | |
− | + | printf("CTRL-A\nCTRL-C\nCTRL-V\nCTRL-V\nCTRL-V\nCTRL-V\n"); | |
− | + | break; | |
− | + | case 4: | |
− | + | print(prin, n-7); | |
− | + | printf("CTRL-A\nCTRL-C\nCTRL-V\nCTRL-V\nCTRL-V\nCTRL-V\nCTRL-V\n"); | |
− | + | } | |
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
} | } | ||
Line 226: | Line 185: | ||
{{Template:FBD}} | {{Template:FBD}} | ||
+ | |||
+ | [[Category:Placement Coding Questions from Arrays]] |
Imagine you have a special keyboard with the following keys:
A
Ctrl+A
Ctrl+C
Ctrl+V
where CTRL+A, CTRL+C, CTRL+V each acts as one function key for “Select All”, “Copy”, and “Paste” operations respectively.
If you can only press the keyboard for N times (with the above four keys), please write a program to produce maximum numbers of A. If possible, please also print out the sequence of keys. That is to say, the input parameter is N (No. of keys that you can press), the output is M (No. of As that you can produce).
A key to the solution is that we can continue pressing CTRL-V multiple times and the characters in the buffer will get printed continuously. The recurrence relation for the solution is
sol[n] = max(2 * sol[n-3], 3 * sol[n-4], 4 * sol[n-5]) | n > 6
and
1 for 1<= n <= 6
The recurrence relation is drawn from the fact that, the optimal solution at position $n$ will be obtained by CTRL-A, CTRL-C, CTRL-V sequence starting at either $(n-3)^{th}$ position or $(n-4)^{th}$ position or $(n-5)^{th}$ position. We needn't consider solution at position $(n-6)$ because that is already considered while calculating the solution at position $(n-3)$ which we are considering. Each CTRL-V prints the same number of characters as was on the screen during which the previous CTRL-A was typed. So, if we take $sol[n-3]$, that would mean CTRL-A starting at $n-2$, CTRL-C at $n-1$ and CTRL-V at $n$. So, $sol[n-3]$ is doubled at $n$. If we take $sol[n-4]$, there will be CTRL-V at positions $n-1$ and $n$, and so $sol[n]$ becomes $3$ times $sol[n-4]$. Similarly, if we take $sol[n-5]$, there will be 3 CTRL-V at $n-2$, $n-1$ and $n$ and $sol[n]$ becomes 4 times $sol[n-5]$.
<syntaxhighlight lang="c" name="printa">
//Returns max of a,b,c int max(int a, int b, int c) { return a > b ? a > c? a:c : b > c? b:c; }
//Returns 1 if a = max(a,b,c), 2 if b = max(a,b,c) and 3 if c = max(a,b,c) int maxp(int a, int b, int c) { return a > b ? a > c? 1:3 : b > c? 2:3; }
void print(int *, int);
int main() { unsigned int n, i; unsigned long long sol[1000]; unsigned int prin[1000]; printf("Enter N: "); scanf("%u", &n);
for(i = 1 ;n>5? i<=5: i<= n; i++) { sol[i] = i; prin[i] = 0; } if(n >= 6) { sol[6] = 6; prin[6] = 1; } for(i = 7; i <= n; i++) { sol[i] = max(2 * sol[i-3], 3 * sol[i-4], 4 * sol[i-5]); prin[i] = maxp(2 * sol[i-3], 3 * sol[i-4], 4 * sol[i-5]); } printf("M = %llu\n", sol[n]); printf("Enter any char to start printing the key sequence: \n"); scanf("%d", &n); printf("Printing the sequence: \n\n"); print(prin, n); }
void print(int * prin, int n) { if(n < 1) return; switch(prin[n]) { case 0: print(prin, n-1); printf("A\n"); break; case 1: print(prin, n-3); printf("CTRL-A\nCTRL-C\nCTRL-V\n"); break; case 2: print(prin, n-4); printf("CTRL-A\nCTRL-C\nCTRL-V\nCTRL-V\n"); break; case 3: print(prin, n-5); printf("CTRL-A\nCTRL-C\nCTRL-V\nCTRL-V\n"); } }
</syntaxhighlight>
The above solution assumes that after CTRL-C, we can do a mouse click as otherwise CTRL-V will override whatever was selected on the screen. If mouse click is not allowed, recurrence relation should be modified as:
sol[n] = max(2 * sol[n-4], 3 * sol[n-5], 4 * sol[n-6], 5 * sol[n-7]) | n > 7
and
1 for 1<= n <= 7
The code for this will be: <syntaxhighlight lang="c" name="printa2">
//Returns max of a,b,c,d int max(int a, int b, int c, int d) {
return a > b ? a > c? a > d ? a : d : c > d? c : d : b > c? b > d? b : d : c > d? c : d ;
}
//Returns 1 if a = max(a,b,c,d), 2 if b = max(a,b,c,d), 3 if c = max(a,b,c,d) and 4 if d = max(a,b,c,d)
int maxp(int a, int b, int c, int d)
{
return a > b ? a > c? a > d ? 1 : 4 : c > d? 3 : 4 : b > c? b > d? 2 : 4 : c > d? 3 : 4;
}
void print(int *, int);
int main() { unsigned int n, i; unsigned long long sol[1000]; unsigned int prin[1000]; printf("Enter N: "); scanf("%u", &n);
for(i = 1 ;n>7? i<=7: i<= n; i++) { sol[i] = i; prin[i] = 0; }
for(i = 8; i <= n; i++) { sol[i] = max( 2 * sol[i-4], 3 * sol[i-5], 4 * sol [i-6], 5 * sol[i-7]); prin[i] = maxp( 2 * sol[i-4], 3 * sol[i-5], 4 * sol [i-6], 5 * sol[i-7]); } printf("M = %llu\n", sol[n]); printf("Enter any char to start printing the key sequence: \n"); scanf("%d", &n); printf("Printing the sequence: \n\n"); print(prin, n); }
void print(int * prin, int n) { if(n < 1) return; switch(prin[n]) { case 0: print(prin, n-1); printf("A\n"); break; case 1: print(prin, n-4); printf("CTRL-A\nCTRL-C\nCTRL-V\nCTRL-V\n"); break; case 2: print(prin, n-5); printf("CTRL-A\nCTRL-C\nCTRL-V\nCTRL-V\nCTRL-V\n"); break; case 3: print(prin, n-6); printf("CTRL-A\nCTRL-C\nCTRL-V\nCTRL-V\nCTRL-V\nCTRL-V\n");
break; case 4: print(prin, n-7);
printf("CTRL-A\nCTRL-C\nCTRL-V\nCTRL-V\nCTRL-V\nCTRL-V\nCTRL-V\n"); } }
</syntaxhighlight>
Imagine you have a special keyboard with the following keys:
A
Ctrl+A
Ctrl+C
Ctrl+V
where CTRL+A, CTRL+C, CTRL+V each acts as one function key for “Select All”, “Copy”, and “Paste” operations respectively.
If you can only press the keyboard for N times (with the above four keys), please write a program to produce maximum numbers of A. If possible, please also print out the sequence of keys. That is to say, the input parameter is N (No. of keys that you can press), the output is M (No. of As that you can produce).
<syntaxhighlight lang="c" name="printa">
int main() {
unsigned int N, i, j; unsigned long long M; unsigned long long sol[1000]; unsigned long long buf[3]; unsigned int ind[1000]; printf("Enter N: "); scanf("%lu", &N); unsigned long long arr[3]; memset(arr, 0, 3*sizeof(arr[0])); memset(sol, 0, 1000*sizeof(sol[0])); /* arr[0] = 4; buf[0] = 1; arr[1] = 6; buf[1] = 2; arr[2] = 6; buf[2] = 3; */ arr[0] = 4; buf[0] = 1; arr[1] = 6; buf[1] = 2; arr[2] = 6; buf[2] = 3; unsigned index; char * out[] = { "A\n", "CTRL+A\n", "CTRL+C\n", "CTRL+V\n"}; unsigned int outf[1000]; unsigned p = 2, pp = 3; memset(outf, 0, 1000*sizeof(outf[0])); for(i=1; i<=N; i++) { if(i <= 6) { outf[i] = 0; sol[i] = i; ind[i] = 0; ind[6] = 3; } else { printf("\n\ni = %u\n", i); arr[0] = arr[1] + buf[1]; arr[1] = arr[2] + buf[2]; arr[2] = 2 * sol[i-3]; buf[0] = buf[1]; buf[1] = buf[2]; buf[2] = sol[i-3]; if(arr[0] > arr[1]) { if(arr[0] > arr[2]) { index = i-5; sol[i] = arr[0]; // outf[i] = outf[i-1]; //outf[i-1] = outf[i-2]; if(p > 3){ outf[p+1] = 1; outf[p+2] = 2; } // for(j = 0; j < buf[0]; j++) // outf[j] = 0; for(j = p+3; j <=i; j++) outf[j] = 3; ind[i] = p; if(ind[p] >= 3){ outf[ind[p]+1] = 1; outf[ind[p]+2] = 2; } for(j = ind[p]+3; j <= p; j++) outf[j] = 3; } else { index = i-3; sol[i] = arr[2]; outf[i] = 3; outf[i-1] = 2; outf[i-2] = 1; outf[i-1] = 2; outf[i-2] = 1; ind[i] = i-3; outf[ind[i-3]+1] = 1; outf[ind[i-3]+2] = 2; for(j = ind[i-3]+3; j < i-3; j++) { outf[j] = 3; } // p = pp; // pp = i -3; // printf("CTRL+A\nCTRL+C\nCTRL+V\n"); } } else if (arr[1] > arr[2]) { index = i-4; sol[i] = arr[1]; outf[pp+1] = 1; outf[pp+2] = 2; // for(j = 0; j < buf[1]; j++) // outf[j] = 0; for(j = pp+3; j <=i; j++) outf[j] = 3; ind[i] = pp; if(ind[pp] >= 3){ outf[ind[pp]+1] = 1; outf[ind[pp]+2] = 2; } for(j = ind[pp]+3; j <= pp; j++) outf[j] = 3; //outf[i-1] = outf[i-2]; //outf[i-2]= outf[i-3]; //printf("CTRL+V\n"); } else { index = i-3; sol[i] = arr[2]; outf[i] = 3; outf[i-1] = 2; outf[i-2] = 1; ind[i] = i-3; outf[ind[i-3]+1] = 1; outf[ind[i-3]+2] = 2; for(j = ind[i-3]+3; j < i-3; j++) { outf[j] = 3; } //p = pp; // pp = i -3; //printf("CTRL+A\nCTRL+C\nCTRL+V\n"); } // sol[i] = max(arr[0] , arr[1], arr[2]); printf("\n%lld %lld %lld\n", arr[0], arr[1], arr[2]); printf("%lld %lld %lld\n", buf[0], buf[1], buf[2]); printf("p = %u pp = %u\n", p, pp); for(j = 1; j <= i; j++) { // printf(out[outf[j]]); } p = pp; pp = i - 3; } } i = 1; while(i+1 < N && outf[i+1] != 2) { outf[i] = 0; i++; } printf("\n\nKey Sequences:\n\n"); // if(N <= 6) { // printf("A\nA\nA\nA\nA\nA\n"); } //else { for(i = 1; i <= N; i++) { printf(out[outf[i]]); } } for(i = 1; i <= N; i++) { printf("%u ",ind[i]); } printf("\nM = %llu\n", sol[N]);
}
</syntaxhighlight>