Mixing
Why is there a difference between two similar implementations of a 'for' loop?
I'm trying to write an insertion sort method, and I have managed to finish it, but I don't understand why my first version cannot work correctly.
Here's my first attempt:
public static void insertionSort(int list) {
for (int i = 1; i < list.length; i++) {
int current = list[i];
for (int k = i - 1; k >= 0 && current < list[k]; k--) {
list[i] = list[k];
list[k] = current;
}
}
}
public static void main(String args) {
int list = {8, 22, 90, 10};
insertionSort(list);
}
My output for the above code is: 8, 10, 10, 22
But the answer would be correct if the inside for-loop, at line 5, is changed from: list[i] = list[k]; to: list[k + 1] = list[k];
To my understanding, k + 1 is equal to i, but it must be different in loop counting and I can't figure out how. I have tried many sets of input, and only values that lie between the range of the 2 first indexes (in this case 8 and 22) would be incorrect.
java
edited Jan 2 at 16:11
Peter Mortensen
13.5k1984111
asked Jan 2 at 9:12
nglunglu
413
add a comment |
I'm trying to write an insertion sort method, and I have managed to finish it, but I don't understand why my first version cannot work correctly.
Here's my first attempt:
public static void insertionSort(int list) {
for (int i = 1; i < list.length; i++) {
int current = list[i];
for (int k = i - 1; k >= 0 && current < list[k]; k--) {
list[i] = list[k];
list[k] = current;
}
}
}
public static void main(String args) {
int list = {8, 22, 90, 10};
insertionSort(list);
}
My output for the above code is: 8, 10, 10, 22
But the answer would be correct if the inside for-loop, at line 5, is changed from: list[i] = list[k]; to: list[k + 1] = list[k];
To my understanding, k + 1 is equal to i, but it must be different in loop counting and I can't figure out how. I have tried many sets of input, and only values that lie between the range of the 2 first indexes (in this case 8 and 22) would be incorrect.
java
edited Jan 2 at 16:11
Peter Mortensen
13.5k1984111
asked Jan 2 at 9:12
nglunglu
413
add a comment |
I'm trying to write an insertion sort method, and I have managed to finish it, but I don't understand why my first version cannot work correctly.
Here's my first attempt:
public static void insertionSort(int list) {
for (int i = 1; i < list.length; i++) {
int current = list[i];
for (int k = i - 1; k >= 0 && current < list[k]; k--) {
list[i] = list[k];
list[k] = current;
}
}
}
public static void main(String args) {
int list = {8, 22, 90, 10};
insertionSort(list);
}
My output for the above code is: 8, 10, 10, 22
But the answer would be correct if the inside for-loop, at line 5, is changed from: list[i] = list[k]; to: list[k + 1] = list[k];
To my understanding, k + 1 is equal to i, but it must be different in loop counting and I can't figure out how. I have tried many sets of input, and only values that lie between the range of the 2 first indexes (in this case 8 and 22) would be incorrect.
java
edited Jan 2 at 16:11
Peter Mortensen
13.5k1984111
asked Jan 2 at 9:12
nglunglu
413
I'm trying to write an insertion sort method, and I have managed to finish it, but I don't understand why my first version cannot work correctly.
Here's my first attempt:
public static void insertionSort(int list) {
for (int i = 1; i < list.length; i++) {
int current = list[i];
for (int k = i - 1; k >= 0 && current < list[k]; k--) {
list[i] = list[k];
list[k] = current;
}
}
}
public static void main(String args) {
int list = {8, 22, 90, 10};
insertionSort(list);
}
My output for the above code is: 8, 10, 10, 22
But the answer would be correct if the inside for-loop, at line 5, is changed from: list[i] = list[k]; to: list[k + 1] = list[k];
To my understanding, k + 1 is equal to i, but it must be different in loop counting and I can't figure out how. I have tried many sets of input, and only values that lie between the range of the 2 first indexes (in this case 8 and 22) would be incorrect.
java
java
edited Jan 2 at 16:11
Peter Mortensen
13.5k1984111
asked Jan 2 at 9:12
nglunglu
413
edited Jan 2 at 16:11
Peter Mortensen
13.5k1984111
asked Jan 2 at 9:12
nglunglu
413
edited Jan 2 at 16:11
Peter Mortensen
13.5k1984111
edited Jan 2 at 16:11
Peter Mortensen
13.5k1984111
edited Jan 2 at 16:11
Peter Mortensen
13.5k1984111
13.5k1984111
asked Jan 2 at 9:12
nglunglu
413
asked Jan 2 at 9:12
nglunglu
413
asked Jan 2 at 9:12
nglunglu
413
413
add a comment |
add a comment |
1 Answer
1
active
oldest
votes
k + 1 is equal to i, but only in the first iteration of the inner for loop. int k = i - 1 is only run once per iteration of the outer for loop.
In the second iteration of the inner for loop, k is decremented but i is not. Therefore, k + 1 and i are not interchangeable inside the inner for loop.
// second iteration of the outer for loop, second iteration of the inner for loop:
list[i] = list[k]; // means "list[2] = list[0]
// whereas
list[k + 1] = list[k]; // means "list[1] = list[0]"
answered Jan 2 at 9:16
SweeperSweeper
65.1k1071139
k is iterated down, k-- not k++.
– Sagi Rika
Jan 2 at 9:18
@SagiRika Oops! fixed.
– Sweeper
Jan 2 at 9:19
give a code example for clarity and I think this should be accepted as answer.
– Murat Güvenç
Jan 2 at 9:22
@MuratGüvenç Is it clearer now?
– Sweeper
Jan 2 at 9:26
I think it is :) It is up to @nglu to accept this.
– Murat Güvenç
Jan 2 at 10:03
add a comment |
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1 Answer
1
active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
k + 1 is equal to i, but only in the first iteration of the inner for loop. int k = i - 1 is only run once per iteration of the outer for loop.
In the second iteration of the inner for loop, k is decremented but i is not. Therefore, k + 1 and i are not interchangeable inside the inner for loop.
// second iteration of the outer for loop, second iteration of the inner for loop:
list[i] = list[k]; // means "list[2] = list[0]
// whereas
list[k + 1] = list[k]; // means "list[1] = list[0]"
answered Jan 2 at 9:16
SweeperSweeper
65.1k1071139
k is iterated down, k-- not k++.
– Sagi Rika
Jan 2 at 9:18
@SagiRika Oops! fixed.
– Sweeper
Jan 2 at 9:19
give a code example for clarity and I think this should be accepted as answer.
– Murat Güvenç
Jan 2 at 9:22
@MuratGüvenç Is it clearer now?
– Sweeper
Jan 2 at 9:26
I think it is :) It is up to @nglu to accept this.
– Murat Güvenç
Jan 2 at 10:03
add a comment |
k + 1 is equal to i, but only in the first iteration of the inner for loop. int k = i - 1 is only run once per iteration of the outer for loop.
In the second iteration of the inner for loop, k is decremented but i is not. Therefore, k + 1 and i are not interchangeable inside the inner for loop.
// second iteration of the outer for loop, second iteration of the inner for loop:
list[i] = list[k]; // means "list[2] = list[0]
// whereas
list[k + 1] = list[k]; // means "list[1] = list[0]"
answered Jan 2 at 9:16
SweeperSweeper
65.1k1071139
k is iterated down, k-- not k++.
– Sagi Rika
Jan 2 at 9:18
@SagiRika Oops! fixed.
– Sweeper
Jan 2 at 9:19
give a code example for clarity and I think this should be accepted as answer.
– Murat Güvenç
Jan 2 at 9:22
@MuratGüvenç Is it clearer now?
– Sweeper
Jan 2 at 9:26
I think it is :) It is up to @nglu to accept this.
– Murat Güvenç
Jan 2 at 10:03
add a comment |
k + 1 is equal to i, but only in the first iteration of the inner for loop. int k = i - 1 is only run once per iteration of the outer for loop.
In the second iteration of the inner for loop, k is decremented but i is not. Therefore, k + 1 and i are not interchangeable inside the inner for loop.
// second iteration of the outer for loop, second iteration of the inner for loop:
list[i] = list[k]; // means "list[2] = list[0]
// whereas
list[k + 1] = list[k]; // means "list[1] = list[0]"
answered Jan 2 at 9:16
SweeperSweeper
65.1k1071139
k + 1 is equal to i, but only in the first iteration of the inner for loop. int k = i - 1 is only run once per iteration of the outer for loop.
In the second iteration of the inner for loop, k is decremented but i is not. Therefore, k + 1 and i are not interchangeable inside the inner for loop.
// second iteration of the outer for loop, second iteration of the inner for loop:
list[i] = list[k]; // means "list[2] = list[0]
// whereas
list[k + 1] = list[k]; // means "list[1] = list[0]"
answered Jan 2 at 9:16
SweeperSweeper
65.1k1071139
edited Jan 2 at 9:25
answered Jan 2 at 9:16
SweeperSweeper
65.1k1071139
answered Jan 2 at 9:16
SweeperSweeper
65.1k1071139
answered Jan 2 at 9:16
SweeperSweeper
65.1k1071139
65.1k1071139
k is iterated down, k-- not k++.
– Sagi Rika
Jan 2 at 9:18
@SagiRika Oops! fixed.
– Sweeper
Jan 2 at 9:19
give a code example for clarity and I think this should be accepted as answer.
– Murat Güvenç
Jan 2 at 9:22
@MuratGüvenç Is it clearer now?
– Sweeper
Jan 2 at 9:26
I think it is :) It is up to @nglu to accept this.
– Murat Güvenç
Jan 2 at 10:03
add a comment |
k is iterated down, k-- not k++.
– Sagi Rika
Jan 2 at 9:18
@SagiRika Oops! fixed.
– Sweeper
Jan 2 at 9:19
give a code example for clarity and I think this should be accepted as answer.
– Murat Güvenç
Jan 2 at 9:22
@MuratGüvenç Is it clearer now?
– Sweeper
Jan 2 at 9:26
I think it is :) It is up to @nglu to accept this.
– Murat Güvenç
Jan 2 at 10:03
k is iterated down, k-- not k++.
– Sagi Rika
Jan 2 at 9:18
k is iterated down, k-- not k++.
– Sagi Rika
Jan 2 at 9:18
@SagiRika Oops! fixed.
– Sweeper
Jan 2 at 9:19
@SagiRika Oops! fixed.
– Sweeper
Jan 2 at 9:19
give a code example for clarity and I think this should be accepted as answer.
– Murat Güvenç
Jan 2 at 9:22
give a code example for clarity and I think this should be accepted as answer.
– Murat Güvenç
Jan 2 at 9:22
@MuratGüvenç Is it clearer now?
– Sweeper
Jan 2 at 9:26
@MuratGüvenç Is it clearer now?
– Sweeper
Jan 2 at 9:26
I think it is :) It is up to @nglu to accept this.
– Murat Güvenç
Jan 2 at 10:03
I think it is :) It is up to @nglu to accept this.
– Murat Güvenç
Jan 2 at 10:03
add a comment |
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