str

Author: idf

src/ReverseWordsinaString/Solution.java

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+package ReverseWordsinaString;
+
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.List;
+import java.util.stream.Collectors;
+
+/**
+ * User: Danyang
+ * Date: 1/28/2015
+ * Time: 12:19
+ *
+ * Given an input string, reverse the string word by word.
+
+ For example,
+ Given s = "the sky is blue",
+ return "blue is sky the".
+ */
+public class Solution {
+    public String reverseWords(String s) {
+        List<String> lst = Arrays.asList(s.trim().split("\\s+"));
+        Collections.reverse(lst);
+        return lst.stream().collect(Collectors.joining(" "));
+    }
+}

src/SimplifyPath/Solution.java

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+package SimplifyPath;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+import java.util.stream.Collectors;
+
+/**
+ * User: Danyang
+ * Date: 1/28/2015
+ * Time: 12:31
+ * Given an absolute path for a file (Unix-style), simplify it.
+
+ For example,
+ path = "/home/", => "/home"
+ path = "/a/./b/../../c/", => "/c"
+ */
+public class Solution {
+    public String simplifyPath(String path) {
+        List<String> lst = Arrays.asList(path.split("/"));
+        List<String> stk = new ArrayList<>();
+        for(String elt: lst) {
+            if(elt.equals(".")) {
+                continue;
+            }
+            else if(elt.equals("..")) {
+                if(!stk.isEmpty())
+                    stk.remove(stk.size()-1);
+            }
+            else if(elt.length()>0) {
+                stk.add(elt);
+            }
+        }
+        return "/"+stk.stream().collect(Collectors.joining("/"));
+    }
+
+    public static void main(String[] args) {
+        String ret = new Solution().simplifyPath("/..");
+        assert  ret.equals("/");
+    }
+}

src/ZigZagConversion/Solution.java

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+package ZigZagConversion;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.stream.Collectors;
+
+/**
+ * User: Danyang
+ * Date: 1/28/2015
+ * Time: 11:24
+ *
+ * he string "PAYPALISHIRING" is written in a zigzag pattern on a given number of rows like this: (you may want to
+ * display this pattern in a fixed font for better legibility)
+
+ P   A   H   N
+ A P L S I I G
+ Y   I   R
+ And then read line by line: "PAHNAPLSIIGYIR"
+ Write the code that will take a string and make this conversion given a number of rows:
+
+ string convert(string text, int nRows);
+ convert("PAYPALISHIRING", 3) should return "PAHNAPLSIIGYIR".
+ */
+public class Solution {
+    /**
+     * Notice:
+     * 1. new ArrayList<>(n); // initialize array with length n, but not the object itself
+     * @param s
+     * @param nRows
+     * @return
+     */
+    public String convert(String s, int nRows) {
+        List<StringBuilder> rows = new ArrayList<>();
+        for(int i=0; i<nRows; i++)
+            rows.add(new StringBuilder());
+        if(nRows==1)
+            return s;
+        char[] cs = s.toCharArray();
+        for(int i=0; i<cs.length; i++) {
+            int pos = i%(2*nRows-2);
+            if(pos<nRows)
+                rows.get(pos).append(cs[i]);
+            else
+                rows.get(2*nRows-2-pos).append(cs[i]);
+        }
+        return rows.stream().map(StringBuilder::toString).collect(Collectors.joining());
+    }
+
+    public static void main(String[] args) {
+        String ret = new Solution().convert("A", 2);
+        System.out.println(ret);
+    }
+}