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左程云左程云
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2 files changed

+149
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lines changed

‎src/topinterviewquestions/Problem_0008_StringToInteger.java

+15-9
Original file line numberDiff line numberDiff line change
@@ -2,30 +2,32 @@
22

33
public class Problem_0008_StringToInteger {
44

5-
public static int myAtoi(String str) {
6-
if (str == null || str.equals("")) {
5+
public static int myAtoi(String s) {
6+
if (s == null || s.equals("")) {
77
return 0;
88
}
9-
str = removeHeadZero(str.trim());
10-
if (str == null || str.equals("")) {
9+
s = removeHeadZero(s.trim());
10+
if (s == null || s.equals("")) {
1111
return 0;
1212
}
13-
char[] chas = str.toCharArray();
14-
if (!isValid(chas)) {
13+
char[] str = s.toCharArray();
14+
if (!isValid(str)) {
1515
return 0;
1616
}
17-
boolean posi = chas[0] == '-' ? false : true;
17+
// str 是符合日常书写的，正经整数形式
18+
boolean posi = str[0] == '-' ? false : true;
1819
int minq = Integer.MIN_VALUE / 10;
1920
int minr = Integer.MIN_VALUE % 10;
2021
int res = 0;
2122
int cur = 0;
22-
for (int i = (chas[0] == '-' || chas[0] == '+') ? 1 : 0; i < chas.length; i++) {
23-
cur = '0' - chas[i];
23+
for (int i = (str[0] == '-' || str[0] == '+') ? 1 : 0; i < str.length; i++) {
24+
cur = '0' - str[i];
2425
if ((res < minq) || (res == minq && cur < minr)) {
2526
return posi ? Integer.MAX_VALUE : Integer.MIN_VALUE;
2627
}
2728
res = res * 10 + cur;
2829
}
30+
// res 负
2931
if (posi && res == Integer.MIN_VALUE) {
3032
return Integer.MAX_VALUE;
3133
}
@@ -40,12 +42,15 @@ public static String removeHeadZero(String str) {
4042
break;
4143
}
4244
}
45+
// s 到了第一个不是'0'字符的位置
4346
int e = -1;
47+
// 左<-右
4448
for (int i = str.length() - 1; i >= (r ? 1 : 0); i--) {
4549
if (str.charAt(i) < '0' || str.charAt(i) > '9') {
4650
e = i;
4751
}
4852
}
53+
// e 到了最左的 不是数字字符的位置
4954
return (r ? String.valueOf(str.charAt(0)) : "") + str.substring(s, e == -1 ? str.length() : e);
5055
}
5156

@@ -56,6 +61,7 @@ public static boolean isValid(char[] chas) {
5661
if ((chas[0] == '-' || chas[0] == '+') && chas.length == 1) {
5762
return false;
5863
}
64+
// 0 +... -... num
5965
for (int i = 1; i < chas.length; i++) {
6066
if (chas[i] < '0' || chas[i] > '9') {
6167
return false;

‎src/topinterviewquestions/Problem_0010_RegularExpressionMatching.java

+134-15
Original file line numberDiff line numberDiff line change
@@ -2,7 +2,140 @@
22

33
public class Problem_0010_RegularExpressionMatching {
44

5-
public static boolean isMatch(String str, String exp) {
5+
public static boolean isMatch1(String s, String p) {
6+
if (s == null || p == null) {
7+
return false;
8+
}
9+
char[] str = s.toCharArray();
10+
char[] pattern = p.toCharArray();
11+
return isValid(str, pattern) && process(str, pattern, 0, 0);
12+
}
13+
14+
public static boolean isValid(char[] str, char[] pattern) {
15+
for (char cha : str) {
16+
if (cha == '.' || cha == '*') {
17+
return false;
18+
}
19+
}
20+
for (int i = 0; i < pattern.length; i++) {
21+
if (pattern[i] == '*' && (i == 0 || pattern[i - 1] == '*')) {
22+
return false;
23+
}
24+
}
25+
return true;
26+
}
27+
28+
// str[si.....] 能否被 pattern[pi...] 变出来
29+
// 潜台词：pi位置，pattern[pi] != '*'
30+
public static boolean process(char[] str, char[] pattern, int si, int pi) {
31+
if (si == str.length) { // si越界了
32+
if (pi == pattern.length) {
33+
return true;
34+
}
35+
if (pi + 1 < pattern.length && pattern[pi + 1] == '*') {
36+
return process(str, pattern, si, pi + 2);
37+
}
38+
return false;
39+
}
40+
// si 没越界
41+
if (pi == pattern.length) {
42+
return si == str.length;
43+
}
44+
// si 没越界 pi 没越界
45+
if (pi + 1 >= pattern.length || pattern[pi + 1] != '*') {
46+
return ((str[si] == pattern[pi]) || (pattern[pi] == '.')) && process(str, pattern, si + 1, pi + 1);
47+
}
48+
// si 没越界 pi 没越界 pi+1 *
49+
if (pattern[pi] != '.' && str[si] != pattern[pi]) {
50+
return process(str, pattern, si, pi + 2);
51+
}
52+
if (process(str, pattern, si, pi + 2)) {
53+
return true;
54+
}
55+
while (si < str.length && (str[si] == pattern[pi] || pattern[pi] == '.')) {
56+
if (process(str, pattern, si + 1, pi + 2)) {
57+
return true;
58+
}
59+
si++;
60+
}
61+
return false;
62+
}
63+
64+
public static boolean isMatch2(String s, String p) {
65+
if (s == null || p == null) {
66+
return false;
67+
}
68+
char[] str = s.toCharArray();
69+
char[] pattern = p.toCharArray();
70+
int[][] dp = new int[str.length + 1][pattern.length + 1];
71+
for (int si = 0; si <= str.length; si++) {
72+
for (int pi = 0; pi <= pattern.length; pi++) {
73+
dp[si][pi] = -1;
74+
}
75+
}
76+
// dp[si][pi] == -1
77+
// dp[si][pi] == 0 si pi false
78+
// dp[si][pi] == 1 si pi true
79+
return isValid(str, pattern) && process2(str, pattern, 0, 0, dp);
80+
}
81+
82+
// str[si.....] 能否被 pattern[pi...] 变出来
83+
// 潜台词：pi位置，pattern[pi] != '*'
84+
public static boolean process2(char[] str, char[] pattern, int si, int pi, int[][] dp) {
85+
if (dp[si][pi] != -1) {
86+
return dp[si][pi] == 1;
87+
}
88+
// si pi 这个参数组合第一次算
89+
90+
if (si == str.length) { // si越界了
91+
if (pi == pattern.length) {
92+
dp[si][pi] = 1;
93+
return true;
94+
}
95+
// (pi pi+1) pi+2 ....
96+
if (pi + 1 < pattern.length && pattern[pi + 1] == '*') {
97+
boolean ans = process2(str, pattern, si, pi + 2, dp);
98+
dp[si][pi] = ans ? 1 : 0;
99+
return ans;
100+
}
101+
dp[si][pi] = 0;
102+
return false;
103+
}
104+
// si 没越界
105+
if (pi == pattern.length) {
106+
boolean ans = si == str.length;
107+
dp[si][pi] = ans ? 1 : 0;
108+
return ans;
109+
}
110+
// si 没越界 pi 没越界
111+
if (pi + 1 >= pattern.length || pattern[pi + 1] != '*') {
112+
boolean ans = ((str[si] == pattern[pi]) || (pattern[pi] == '.'))
113+
&& process2(str, pattern, si + 1, pi + 1, dp);
114+
dp[si][pi] = ans ? 1 : 0;
115+
return ans;
116+
}
117+
// si 没越界 pi 没越界 pi+1 *
118+
if (pattern[pi] != '.' && str[si] != pattern[pi]) {
119+
boolean ans = process2(str, pattern, si, pi + 2, dp);
120+
dp[si][pi] = ans ? 1 : 0;
121+
return ans;
122+
}
123+
if (process2(str, pattern, si, pi + 2, dp)) {
124+
dp[si][pi] = 1;
125+
return true;
126+
}
127+
while (si < str.length && (str[si] == pattern[pi] || pattern[pi] == '.')) {
128+
if (process2(str, pattern, si + 1, pi + 2, dp)) {
129+
dp[si][pi] = 1;
130+
return true;
131+
}
132+
si++;
133+
}
134+
dp[si][pi] = 0;
135+
return false;
136+
}
137+
138+
public static boolean isMatch3(String str, String exp) {
6139
if (str == null || exp == null) {
7140
return false;
8141
}
@@ -34,20 +167,6 @@ public static boolean isMatch(String str, String exp) {
34167
return dp[0][0];
35168
}
36169

37-
public static boolean isValid(char[] s, char[] e) {
38-
for (int i = 0; i < s.length; i++) {
39-
if (s[i] == '*' || s[i] == '.') {
40-
return false;
41-
}
42-
}
43-
for (int i = 0; i < e.length; i++) {
44-
if (e[i] == '*' && (i == 0 || e[i - 1] == '*')) {
45-
return false;
46-
}
47-
}
48-
return true;
49-
}
50-
51170
public static boolean[][] initDPMap(char[] s, char[] e) {
52171
int slen = s.length;
53172
int elen = e.length;

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