revisit some easy / mid questions

Author: metanet

src/problems/leetcode/ContainerWithMostWater.java

@@ -1,11 +1,52 @@
 package problems.leetcode;
 
+import java.util.Map;
+import java.util.TreeMap;
+
 /**
  * https://leetcode.com/problems/container-with-most-water/
  */
 public class ContainerWithMostWater {
 
+    // runtime: O(N)
+    // space: O(1)
     public static int maxArea(int[] height) {
+        if (height == null || height.length < 2) {
+            return 0;
+        }
+
+        int i = 0;
+        int j = height.length - 1;
+        int hl = height[i];
+        int hr = height[j];
+        int maxArea = Math.min(hl, hr) * (j - i);
+
+        while (i < j) {
+            if (hl < hr) {
+                while (i < j && hl >= height[i]) {
+                    i++;
+                }
+                if (i < j) {
+                    hl = height[i];
+                }
+            } else {
+                while (i < j && hr >= height[j]) {
+                    j--;
+                }
+                if (i < j) {
+                    hr = height[j];
+                }
+            }
+
+            if (i < j) {
+                maxArea = Math.max(maxArea, Math.min(hl, hr) * (j - i));
+            }
+        }
+
+        return maxArea;
+    }
+
+    public static int maxArea3(int[] height) {
         if (height == null || height.length == 0) {
             return 0;
         }
@@ -26,6 +67,7 @@ public static int maxArea(int[] height) {
         return maxArea;
     }
 
+    // brute force
     public static int maxArea2(int[] height) {
         int maxArea = 0, maxH = 0;
         for (int i = 0; i < height.length; i++) {
@@ -40,16 +82,17 @@ public static int maxArea2(int[] height) {
                     maxArea = area;
                     maxH = h;
                 }
-                //maxArea = Math.max(maxArea, w * h);
+                // maxArea = Math.max(maxArea, w * h);
             }
         }
 
         return maxArea;
     }
 
     public static void main(String[] args) {
-        int[] heights = {1, 8, 6, 2, 5, 4, 8, 3, 7};
-        System.out.println(maxArea(heights));
+        System.out.println(maxArea(new int[] { 1, 8, 6, 2, 5, 4, 8, 3, 7 }));
+        System.out.println(maxArea(new int[] { 1, 0, 0, 0, 0, 0, 0, 2, 2 }));
+        System.out.println(maxArea(new int[] { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 }));
     }
 
 }

src/problems/leetcode/LongestPalindromicSubstring.java

@@ -6,13 +6,56 @@
 public class LongestPalindromicSubstring {
 
     public static void main(String[] args) {
-        String s = "babadada";
+        // String s = "babadada";
         //        String s = "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000";
-        String longestPal = new LongestPalindromicSubstring().longestPalindrome(s);
-        System.out.println(longestPal);
+        // String longestPal = new LongestPalindromicSubstring().longestPalindrome(s);
+        // System.out.println(longestPal);
+
+        System.out.println(longestPalindrome("ccc"));
+    }
+
+    // runtime: O(N^2)
+    // space: O(N^2)
+    public static String longestPalindrome(String s) {
+        if (s == null || s.length() < 2) {
+            return s;
+        }
+
+        int[][] m = new int[s.length()][s.length()];
+        // base
+        // P(i, i) = true
+        // P(i, i+1) = (Si == Si+1)
+        String result = s.substring(0, 1);
+        for (int i = 0; i < s.length(); i++) {
+            m[i][i] = 1;
+            if (i + 1 < s.length()) {
+                if (s.charAt(i) == s.charAt(i + 1)) {
+                    m[i][i + 1] = 2;
+                    result = s.substring(i, i + 2);
+                } else {
+                    m[i][i + 1] = 0;
+                }
+            }
+        }
+
+        // common
+        // P(i, j) = (P(i + 1, j - 1) + Si == Sj)
+        for (int len = 3; len <= s.length(); len++) {
+            for (int i = 0; i <= s.length() - len; i++) {
+                int j = i + len - 1;
+                int p = m[i + 1][j - 1];
+                m[i][j] = (p != 0 && s.charAt(i) == s.charAt(j)) ? p + 2 : 0;
+                // System.out.println("i=" + i + ", len=" + len + ", p=" + m[i][j]);
+                if (m[i][j] > result.length()) {
+                    result = s.substring(i, i + len);
+                }
+            }
+        }
+
+        return result;
     }
 
-    public String longestPalindrome(String s) {
+    public String longestPalindromeDP(String s) {
         if (s == null || s.length() <= 1) {
             return s;
         }
@@ -54,4 +97,38 @@ public String longestPalindrome(String s) {
         return s.substring(start, start + maxLen);
     }
 
+    // runtime: O(N^3) if the longest palindrome has length of 1
+    // space: O(1)
+    public String longestPalindromeBruteForce(String s) {
+        if (s == null || s.length() < 2) {
+            return s;
+        }
+
+        String result = null;
+        for (int i = 0; i < s.length(); i++) {
+            for (int j = s.length() - 1; j >= i; j--) {
+                String sub = s.substring(i, j + 1);
+                if (result != null && sub.length() <= result.length()) {
+                    continue;
+                } else if (isPalindrome(sub)) {
+                    result = sub;
+                }
+            }
+        }
+
+        return result;
+    }
+
+    private boolean isPalindrome(String s) {
+        int i = 0, j = s.length() - 1;
+        while (i < j) {
+            if (s.charAt(i++) != s.charAt(j--)) {
+                return false;
+            }
+        }
+
+        return true;
+    }
+
+
 }

src/problems/leetcode/LongestSubstringWithoutRepeatingCharacters.java

@@ -10,13 +10,14 @@
  */
 public class LongestSubstringWithoutRepeatingCharacters {
 
+    // runtime: O(N^3)
+    // space: O(N)
     public static int lengthOfLongestSubstringBruteForce(String s) {
         int maxLength = 0;
 
         for (int i = 0; i < s.length(); i++) {
             Set<Character> chars = new HashSet<>();
-            int j = i;
-            for (; j < s.length(); j++) {
+            for (int j = i; j < s.length(); j++) {
                 if (!chars.add(s.charAt(j))) {
                     break;
                 }
@@ -27,6 +28,8 @@ public static int lengthOfLongestSubstringBruteForce(String s) {
         return maxLength;
     }
 
+    // runtime: O(N)
+    // space: O(N)
     public static int lengthOfLongestSubstring(String s) {
         int maxLength = 0, start = 0, n = s.length();
         Map<Character, Integer> indices = new HashMap<>();

src/problems/leetcode/ReverseInteger.java

@@ -6,30 +6,36 @@
 public class ReverseInteger {
 
     public static void main(String[] args) {
-        int x = 34056;
-        System.out.println(reverse(x));
+        // System.out.println(reverse(34056));
+        System.out.println(reverse(1534236469));
     }
 
+    // runtime: O(N)
+    // space: O(1)
     public static int reverse(int x) {
-        long num = Math.abs(x), reverseNum = 0, j = 10, p = 10;
+        if (x == 0) {
+            return x;
+        }
 
-        for (int i = 0; i < 11; i++) {
-            long digit = (num % j) / Math.max((j / 10), 1);
-            if (digit > 0) {
-                reverseNum = reverseNum * p + digit;
-                p = 10;
-            } else {
-                p *= 10;
+        int n = x;
+        if (n < 0) {
+            n *= -1;
+        }
+        int y = 0;
+        while (n > 0) {
+            if (y > 0 && Integer.MAX_VALUE / y < 10) {
+                return 0;
             }
 
-            j *= 10;
+            int d = n % 10;
+            y = d + y * 10;
+            n /= 10;
         }
-
         if (x < 0) {
-            reverseNum = -reverseNum;
+            y *= -1;
         }
 
-        return (reverseNum > Integer.MAX_VALUE || reverseNum < Integer.MIN_VALUE) ? 0 : (int) reverseNum;
+        return y;
     }
 
 }

src/problems/leetcode/StringToIntegerAtoi.java

@@ -6,11 +6,44 @@
 public class StringToIntegerAtoi {
 
     public static void main(String[] args) {
-        String s = "9223372036854775808";
-        System.out.println(myAtoi(s));
+        System.out.println(myAtoi("9223372036854775808"));
     }
 
-    public static int myAtoi(String str) {
+    // runtime: O(N)
+    // space: O(1)
+    public static int myAtoi(String s) {
+        if (s == null || s.isBlank()) {
+            return 0;
+        }
+
+        s = s.trim();
+        int sign = 1;
+        int start = 0;
+        if (s.charAt(0) == '-') {
+            sign = -1;
+            start = 1;
+        } else if (s.charAt(0) == '+') {
+            start = 1;
+        }
+
+        long n = 0;
+        for (int i = start; i < s.length(); i++) {
+            char c = s.charAt(i);
+            if (!Character.isDigit(c)) {
+                break;
+            }
+
+            n = n * 10 + (c - '0');
+            if (n > Integer.MAX_VALUE) {
+                break;
+            }
+        }
+        n *= sign;
+
+        return (int) Math.max(Math.min(n, Integer.MAX_VALUE), Integer.MIN_VALUE);
+    }
+
+    public static int myAtoi2(String str) {
         int sign = 1, i = 0;
         long num = 0;
         while (i < str.length() && str.charAt(i) == ' ') {

src/problems/leetcode/ZigZagConversation.java

@@ -0,0 +1,55 @@
+package problems.leetcode;
+
+import java.util.ArrayList;
+
+// https://leetcode.com/problems/zigzag-conversion/
+public class ZigZagConversation {
+    
+    public static String convert(String s, int numRows) {
+        if (numRows < 2) {
+            return s;
+        }
+        
+        ArrayList<ArrayList<Character>> rows = new ArrayList<ArrayList<Character>>();
+        for (int i = 0; i < numRows; i++) {
+            rows.add(new ArrayList<>());
+        }
+
+        boolean forward = true;
+        for (int i = 0, r = 0; i < s.length(); i++) {
+            rows.get(r).add(s.charAt(i));
+            if (forward) {
+                if (r == numRows - 1) {
+                    r--;
+                    forward = false;
+                } else {
+                    r++;
+                }
+            } else {
+                if (r == 0) {
+                    r++;
+                    forward = true;
+                } else {
+                    r--;
+                }
+            }
+        }
+
+        StringBuilder sb = new StringBuilder();
+
+        for (ArrayList<Character> row : rows) {
+            for (char c : row) {
+                sb.append(c);
+            }
+        }
+
+        return sb.toString();
+    }
+
+    public static void main(String[] args) {
+        System.out.println(convert("PAYPALISHIRING", 3));
+        System.out.println(convert("PAYPALISHIRING", 4));
+        System.out.println(convert("AB", 1));
+    }
+
+}