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Commit 0facc38

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Signed-off-by: begeekmyfriend <begeekmyfriend@gmail.com>
1 parent 5136935 commit 0facc38

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5 files changed

+63
-63
lines changed

5 files changed

+63
-63
lines changed

‎091_decode_ways/decode_ways.c‎

Lines changed: 12 additions & 12 deletions
Original file line numberDiff line numberDiff line change
@@ -2,29 +2,29 @@
22
#include <stdlib.h>
33
#include <string.h>
44

5-
static int numDecodings(char* s) {
5+
6+
static int numDecodings(char* s)
7+
{
68
int len = strlen(s);
79
if (len == 0) {
810
return 0;
911
}
1012

11-
int dp[len + 1];
12-
memset(dp, 0, (len + 1) * sizeof(int));
13-
14-
dp[0] = 1;
15-
dp[1] = s[0] == '0' ? 0 : 1;
13+
int a = 1;
14+
int b = s[0] == '0' ? 0 : a;
15+
int c = b;
16+
/* DP: How many counts in sequence c = f(a, b) and c counts s[i - 1] */
1617
for (int i = 2; i <= len; i++) {
17-
if (s[i - 1] != '0') {
18-
dp[i] = dp[i - 1];
19-
}
20-
18+
c = s[i - 1] == '0' ? 0 : b;
2119
int num = (s[i - 2] - '0') * 10 + (s[i - 1] - '0');
2220
if (num >= 10 && num <= 26) {
23-
dp[i] += dp[i-2];
21+
c += a;
2422
}
23+
a = b;
24+
b = c;
2525
}
2626

27-
return dp[len];
27+
return c;
2828
}
2929

3030
int main(int argc, char **argv)

‎120_triangle/triangle.c‎

Lines changed: 7 additions & 7 deletions
Original file line numberDiff line numberDiff line change
@@ -3,6 +3,7 @@
33
#include <stdbool.h>
44
#include <string.h>
55

6+
67
static int dfs(int** triangle, int row_size, int *col_sizes,
78
int row, int col, int **sums, bool **passes)
89
{
@@ -14,24 +15,23 @@ static int dfs(int** triangle, int row_size, int *col_sizes,
1415
int s1 = dfs(triangle, row_size, col_sizes, row + 1, col, sums, passes);
1516
int s2 = dfs(triangle, row_size, col_sizes, row + 1, col + 1, sums, passes);
1617
sums[row][col] = triangle[row][col] + (s1 < s2 ? s1 : s2);
18+
/* Set pass marks in backtracing as the paths are overlapped */
1719
passes[row][col] = true;
1820
return sums[row][col];
1921
}
2022
}
2123

22-
static int minimumTotal(int** triangle, int triangleRowSize, int *triangleColSizes)
24+
static int minimumTotal(int** triangle, int triangleSize, int *triangleColSizes)
2325
{
2426
int i;
25-
bool **passes = malloc(triangleRowSize * sizeof(bool *));
26-
for (i = 0; i < triangleRowSize; i++) {
27+
int **sums = malloc(triangleSize * sizeof(int *));
28+
bool **passes = malloc(triangleSize * sizeof(bool *));
29+
for (i = 0; i < triangleSize; i++) {
2730
passes[i] = malloc(triangleColSizes[i]);
2831
memset(passes[i], false, triangleColSizes[i]);
29-
}
30-
int **sums = malloc(triangleRowSize * sizeof(int *));
31-
for (i = 0; i < triangleRowSize; i++) {
3232
sums[i] = malloc(triangleColSizes[i] * sizeof(int));
3333
}
34-
return dfs(triangle, triangleRowSize, triangleColSizes, 0, 0, sums, passes);
34+
return dfs(triangle, triangleSize, triangleColSizes, 0, 0, sums, passes);
3535
}
3636

3737
int main(void)

‎207_course_schedule/course_schedule.c‎

Lines changed: 22 additions & 17 deletions
Original file line numberDiff line numberDiff line change
@@ -3,51 +3,49 @@
33
#include <stdbool.h>
44
#include <string.h>
55

6+
67
struct graph_node {
78
int req_num;
89
int reqs[15];
10+
bool touched;
11+
bool taken;
912
};
1013

11-
static bool dfs(struct graph_node *courses, int id, bool*takens, bool*touched)
14+
static bool dfs(struct graph_node *courses, int id)
1215
{
1316
int i;
14-
if (touched[id]) {
17+
if (courses[id].touched) {
1518
return true;
16-
} else if (takens[id]) {
19+
} else if (courses[id].taken) {
1720
return false;
1821
} else {
19-
takens[id] = true;
22+
courses[id].taken = true;
2023
for (i = 0; i < courses[id].req_num; i++) {
21-
if (!dfs(courses, courses[id].reqs[i], takens, touched)) {
24+
if (!dfs(courses, courses[id].reqs[i])) {
2225
return false;
2326
}
2427
}
25-
/* marked as available and no need to traverse next time */
26-
touched[id] = true;
27-
takens[id] = false;
28+
/* If paths overlapped, mark in backtracing for no need to traverse next time */
29+
courses[id].touched = true;
30+
courses[id].taken = false;
2831
return true;
2932
}
3033
}
3134

32-
static bool canFinish(int numCourses, int** prerequisites, int prerequisitesRowSize, int prerequisitesColSize)
35+
static bool canFinish(int numCourses, int** prerequisites, int prerequisitesSize, int *prerequisitesColSize)
3336
{
3437
int i;
35-
bool *takens = malloc(numCourses);
36-
bool *touched = malloc(numCourses);
3738
struct graph_node *courses = malloc(numCourses * sizeof(*courses));
3839

3940
memset(courses, 0, numCourses * sizeof(*courses));
40-
memset(takens, false, numCourses * sizeof(bool));
41-
memset(touched, false, numCourses * sizeof(bool));
42-
43-
for (i = 0; i < prerequisitesRowSize; i++) {
41+
for (i = 0; i < prerequisitesSize; i++) {
4442
int id = prerequisites[i][0];
4543
int req = prerequisites[i][1];
4644
courses[id].reqs[courses[id].req_num++] = req;
4745
}
4846

4947
for (i = 0; i < numCourses; i++) {
50-
if (!dfs(courses, i, takens, touched)) {
48+
if (!dfs(courses, i)) {
5149
return false;
5250
}
5351
}
@@ -59,24 +57,31 @@ int main(void)
5957
{
6058
int i, course_num = 6, pair_num = 6;
6159
int **pairs = malloc(pair_num * sizeof(int *));
60+
int *col_sizes = malloc(pair_num * sizeof(int));
6261
pairs[0] = malloc(2 * sizeof(int));
6362
pairs[0][0] = 1;
6463
pairs[0][1] = 0;
64+
col_sizes[0] = 2;
6565
pairs[1] = malloc(2 * sizeof(int));
6666
pairs[1][0] = 2;
6767
pairs[1][1] = 1;
68+
col_sizes[1] = 2;
6869
pairs[2] = malloc(2 * sizeof(int));
6970
pairs[2][0] = 3;
7071
pairs[2][1] = 2;
72+
col_sizes[2] = 2;
7173
pairs[3] = malloc(2 * sizeof(int));
7274
pairs[3][0] = 1;
7375
pairs[3][1] = 3;
76+
col_sizes[3] = 2;
7477
pairs[4] = malloc(2 * sizeof(int));
7578
pairs[4][0] = 4;
7679
pairs[4][1] = 0;
80+
col_sizes[4] = 2;
7781
pairs[5] = malloc(2 * sizeof(int));
7882
pairs[5][0] = 0;
7983
pairs[5][1] = 5;
80-
printf("%s\n", canFinish(course_num, pairs, pair_num, 2) ? "true" : "false");
84+
col_sizes[5] = 2;
85+
printf("%s\n", canFinish(course_num, pairs, pair_num, col_sizes) ? "true" : "false");
8186
return 0;
8287
}

‎210_course_schedule_ii/course_schedule.c‎

Lines changed: 17 additions & 17 deletions
Original file line numberDiff line numberDiff line change
@@ -3,29 +3,33 @@
33
#include <stdbool.h>
44
#include <string.h>
55

6+
67
struct graph_node {
78
int req_num;
89
int reqs[15];
10+
bool touched;
11+
bool taken;
912
};
1013

11-
static bool dfs(struct graph_node *courses, int id, bool*takens, bool*touched, int *order, int *count)
14+
static bool dfs(struct graph_node *courses, int id, int *order, int *count)
1215
{
1316
int i;
14-
if (touched[id]) {
17+
if (courses[id].touched) {
1518
return true;
16-
} else if (takens[id]) {
19+
} else if (courses[id].taken) {
1720
return false;
1821
} else {
19-
takens[id] = true;
22+
courses[id].taken = true;
2023
for (i = 0; i < courses[id].req_num; i++) {
21-
if (!dfs(courses, courses[id].reqs[i], takens, touched, order, count)) {
24+
if (!dfs(courses, courses[id].reqs[i], order, count)) {
2225
return false;
2326
}
2427
}
25-
/* marked as available and no need to traverse next time */
28+
/* Record path in backtrace before DFS return */
2629
order[(*count)++] = id;
27-
touched[id] = true;
28-
takens[id] = false;
30+
/* If paths overlapped, mark in backtracing for no need to traverse next time */
31+
courses[id].touched = true;
32+
courses[id].taken = false;
2933
return true;
3034
}
3135
}
@@ -34,27 +38,22 @@ static bool dfs(struct graph_node *courses, int id, bool *takens, bool *touched,
3438
* Return an array of size *returnSize.
3539
* Note: The returned array must be malloced, assume caller calls free().
3640
*/
37-
static int *findOrder(int numCourses, int** prerequisites, int prerequisitesRowSize, int prerequisitesColSize, int *returnSize)
41+
static int *findOrder(int numCourses, int** prerequisites, int prerequisitesSize, int *prerequisitesColSize, int *returnSize)
3842
{
3943
int i;
4044
int *order = malloc(numCourses * sizeof(int));
41-
bool *takens = malloc(numCourses);
42-
bool *touched = malloc(numCourses);
4345
struct graph_node *courses = malloc(numCourses * sizeof(*courses));
4446

4547
memset(courses, 0, numCourses * sizeof(*courses));
46-
memset(takens, false, numCourses * sizeof(bool));
47-
memset(touched, false, numCourses * sizeof(bool));
48-
49-
for (i = 0; i < prerequisitesRowSize; i++) {
48+
for (i = 0; i < prerequisitesSize; i++) {
5049
int id = prerequisites[i][0];
5150
int req = prerequisites[i][1];
5251
courses[id].reqs[courses[id].req_num++] = req;
5352
}
5453

5554
*returnSize = 0;
5655
for (i = 0; i < numCourses; i++) {
57-
if (!dfs(courses, i, takens, touched, order, returnSize)) {
56+
if (!dfs(courses, i, order, returnSize)) {
5857
*returnSize = 0;
5958
return order;
6059
}
@@ -67,6 +66,7 @@ int main(void)
6766
{
6867
int i, course_num = 3, pair_num = 1;
6968
int **pairs = malloc(pair_num * sizeof(int *));
69+
int *col_sizes = malloc(pair_num * sizeof(int));
7070
pairs[0] = malloc(2 * sizeof(int));
7171
pairs[0][0] = 1;
7272
pairs[0][1] = 0;
@@ -84,7 +84,7 @@ int main(void)
8484
//pairs[4][1] = 5;
8585

8686
int count = 0;
87-
int *ids = findOrder(course_num, pairs, pair_num, 2, &count);
87+
int *ids = findOrder(course_num, pairs, pair_num, col_sizes, &count);
8888
for (i = 0; i < count; i++) {
8989
printf("%d ", ids[i]);
9090
}

‎236_lowest_common_ancestor_of_a_binary_tree/bst_lca.c‎

Lines changed: 5 additions & 10 deletions
Original file line numberDiff line numberDiff line change
@@ -2,6 +2,7 @@
22
#include <stdlib.h>
33
#include <stdbool.h>
44

5+
56
struct TreeNode {
67
int val;
78
struct TreeNode *left;
@@ -11,24 +12,18 @@ struct TreeNode {
1112
static struct TreeNode* lowestCommonAncestor(struct TreeNode* root, struct TreeNode* p, struct TreeNode* q)
1213
{
1314
if (root == NULL || root == p || root == q) {
15+
/* edge cases: if return NULL then no p or q node in this path */
1416
return root;
1517
}
1618

19+
/* l is the LCA in the left branch but not root->left */
1720
struct TreeNode *l = lowestCommonAncestor(root->left, p, q);
18-
if (l != NULL && l != p && l != q) {
19-
/* both p and q in left subtree: l->left != NULL && l->right != NULL */
20-
return l;
21-
}
22-
21+
/* r is the LCA in the right branch but not root->right */
2322
struct TreeNode *r = lowestCommonAncestor(root->right, p, q);
24-
if (r != NULL && r != p && r != q) {
25-
/* both p and q in right subtree: r->left != NULL && r->right != NULL */
26-
return r;
27-
}
28-
2923
if (l != NULL && r != NULL) {
3024
return root;
3125
} else {
26+
/* if not return root node, the return value is fixed */
3227
return l != NULL ? l : r;
3328
}
3429
}

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