双指针

DFS开头

Author: h2pl

src/DFS/图的连通分量个数.java

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+package DFS;
+
+import java.util.Arrays;
+
+/**
+ * Created by 周杰伦 on 2018/3/30.
+ */
+public class 图的连通分量个数 {
+    static int count = 0;
+    public static int findCircleNum(int[][] M) {
+
+        count = 0;
+        if (M == null)return 0;
+        int m = M.length;
+        int n = M[0].length;
+        int [][]visit = new int[m][n];
+        for (int i = 0;i < visit.length;i ++) {
+            Arrays.fill(visit[i],0);
+        }
+
+        for (int i = 0;i < m;i ++) {
+            for (int j = 0;j < n;j ++) {
+                if (M[i][j] == 1 && visit[i][j] != 1) {
+                    dfs(M, visit, i, j);
+                    count ++;
+                }
+            }
+        }
+        return count;
+    }
+    public static void dfs(int [][]grid,int [][]visit, int x, int y) {
+        if (x < 0 || y < 0 || x >= grid.length || y >= grid[0].length ||grid[x][y] == 0 || visit[x][y] == 1) return;
+
+        visit[x][y] = 1;
+        dfs(grid,visit,x + 1,y);
+        dfs(grid,visit,x,y + 1);
+        dfs(grid,visit,x - 1,y);
+        dfs(grid,visit,x ,y - 1);
+        return;
+    }
+}

src/DFS/查找最大的连通面积.java

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+package DFS;
+
+import java.util.Arrays;
+
+/**
+ * Created by 周杰伦 on 2018/3/30.
+ */
+public class 查找最大的连通面积 {
+    public static void main(String[] args) {
+        int [][]a = {{0,1},{1,1}};
+        System.out.println(maxAreaOfIsland(a));
+    }
+    static int max = 0;
+    static int count = 0;
+    public static int maxAreaOfIsland(int[][] grid) {
+        max = 0;
+        count = 0;
+        if (grid == null)return 0;
+        int m = grid.length;
+        int n = grid[0].length;
+        int [][]visit = new int[m][n];
+        for (int i = 0;i < visit.length;i ++) {
+            Arrays.fill(visit[i],0);
+        }
+
+        for (int i = 0;i < m;i ++) {
+            for (int j = 0;j < n;j ++) {
+                count = 0;
+                if (grid[i][j] == 1) {
+                    dfs(grid, visit, i, j);
+                }
+                if (count > max) max = count;
+            }
+        }
+        return max;
+    }
+    public static void dfs(int [][]grid,int [][]visit, int x, int y) {
+        if (x < 0 || y < 0 || x >= grid.length || y >= grid[0].length ||grid[x][y] == 0 || visit[x][y] == 1) return;
+
+        visit[x][y] = 1;
+        count ++;
+        dfs(grid,visit,x + 1,y);
+        dfs(grid,visit,x,y + 1);
+        dfs(grid,visit,x - 1,y);
+        dfs(grid,visit,x ,y - 1);
+        return;
+    }
+}

src/双指针/两数平方和.java

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+package 双指针;
+
+/**
+ * Created by 周杰伦 on 2018/3/30.
+ */
+public class 两数平方和 {
+    public boolean judgeSquareSum(int c) {
+        double i = 0,j = Math.floor(Math.pow(c,0.5));
+        while (i <= j) {
+            if (i <= j && Math.pow(i,2) + Math.pow(j,2) == c) return true;
+            else if (i <= j && Math.pow(i,2) + Math.pow(j,2) > c) {
+                j --;
+            }
+            else if (i <= j && Math.pow(i,2) + Math.pow(j,2) < c) {
+                i ++;
+            }
+        }
+        return false;
+    }
+}

src/双指针/单链表判环.java

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+package 双指针;
+/**
+ * Definition for singly-linked list.
+
+ * }
+ */
+/**
+ * Created by 周杰伦 on 2018/3/30.
+ */
+
+class ListNode {
+    int val;
+    ListNode next;
+
+    ListNode(int x) {
+        val = x;
+        next = null;
+    }
+}
+public class 单链表判环 {
+
+    public class Solution {
+        public boolean hasCycle(ListNode head) {
+            if (head == null)return false;
+            if (head.next == head) return true;
+            ListNode slow = head;
+            ListNode fast = head;
+            while (slow.next != null && fast.next != null && fast.next.next != null) {
+                slow = slow.next;
+                fast = fast.next.next;
+                if (slow == fast)return true;
+            }
+            return false;
+        }
+    }
+}

src/双指针/反转字符串中的元音字符.java

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+package 双指针;
+
+/**
+ * Created by 周杰伦 on 2018/3/30.
+ */
+public class 反转字符串中的元音字符 {
+    public static void main(String[] args) {
+        String s = "hello";
+        System.out.println(reverseVowels(s));
+    }
+    public static String reverseVowels(String str) {
+        int i = 0,j = str.length() - 1;
+        char[] arr = str.toCharArray();
+        while (i < j) {
+            while (i < j && !vowels(arr[i])) {
+                i ++;
+            }
+            while (i < j && !vowels(arr[j])) {
+                j --;
+            }
+            char temp = arr[i];
+            arr[i] = arr[j];
+            arr[j] = temp;
+            i ++;
+            j --;
+        }
+        return String.valueOf(arr);
+    }
+    public static boolean vowels(char c) {
+        if (c == 'i' || c =='o' || c == 'a' || c =='e' || c == 'u')return true;
+        else if (c == 'I' || c == 'O' || c == 'A' || c == 'E' || c == 'U') return  true;
+        else return false;
+    }
+}

src/双指针/回文字符串.java

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+package 双指针;
+
+/**
+ * Created by 周杰伦 on 2018/3/30.
+ */
+public class 回文字符串 {
+    public static void main(String[] args) {
+        System.out.println(validPalindrome("aba"));
+    }
+    public static boolean validPalindrome(String s) {
+        int i = 0,j = s.length() - 1;
+        while (i < j) {
+            if (s.charAt(i) != s.charAt(j)) {
+                return Palindrome(s,i + 1, j) || Palindrome(s, i, j - 1);
+            }
+            i ++;
+            j --;
+        }
+        return true;
+    }
+    public static boolean Palindrome(String s, int l, int r) {
+        int i = l,j = r;
+        while (i < j) {
+            if (s.charAt(i) != s.charAt(j)) {
+                return false;
+            }
+            i ++;
+            j --;
+        }
+        return true;
+    }
+}

src/双指针/归并两个有序数组.java

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+package 双指针;
+
+/**
+ * Created by 周杰伦 on 2018/3/30.
+ */
+public class 归并两个有序数组 {
+    public void merge(int[] nums1, int m, int[] nums2, int n) {
+        if (nums1.length == 1 && nums2.length == 0) return;
+        if (nums1.length == 1 && nums2 != null)nums1[0] = nums2[0];
+        int i = m - 1,j = n - 1;
+        int index = nums1.length - 1;
+        while (i >= 0 && j >= 0) {
+            if (nums1[i] > nums2[j]) {
+                nums1[index --] = nums1[i];
+                nums1[i] = 0;
+                i --;
+            }
+            else {
+                nums1[index --] = nums2[j];
+                j --;
+            }
+        }
+    }
+
+}

src/双指针/最长子序列加强版.java

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+package 双指针;
+
+import java.lang.reflect.Array;
+import java.util.*;
+
+/**
+ * Created by 周杰伦 on 2018/3/30.
+ */
+public class 最长子序列加强版 {
+    public static void main(String[] args) {
+        List<String> d = new ArrayList<>();
+        d.add("a");
+        d.add("b");
+
+        Collections.sort(d, new Comparator<String>() {
+            @Override
+            public int compare(String o1, String o2) {
+                if (o2.length() == o1.length()) return o1.compareTo(o2);
+                return o2.length() - o1.length();
+            }
+        });
+        System.out.println(Arrays.toString(d.toArray()));
+    }
+    public String findLongestWord(String s, List<String> d) {
+        if (s == null || s.equals(""))return "";
+        if (d == null || d.size() == 0)return "";
+        Collections.sort(d, new Comparator<String>() {
+            @Override
+            public int compare(String o1, String o2) {
+                if (o2.length() == o1.length()) return o1.compareTo(o2);
+                return o2.length() - o1.length();
+            }
+        });
+        for (String sub : d) {
+            int i = 0;
+            int j = 0;
+            while (i < s.length() && j < sub.length()) {
+                if (s.charAt(i) != sub.charAt(j)) {
+                    i ++;
+                }
+                else {
+                    i ++;
+                    j ++;
+                }
+                if (j == sub.length()) {
+                    return sub;
+                }
+            }
+        }
+        return "";
+    }
+}

src/双指针/查找和为9的数对.java

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+package 双指针;
+
+/**
+ * Created by 周杰伦 on 2018/3/29.
+ */
+public class 查找和为9的数对 {
+    public static void main(String[] args) {
+
+    }
+    public int[] twoSum(int[] numbers, int target) {
+        int i = 0,j = numbers.length - 1;
+        int []index = new int[2];
+        while (i < j) {
+            if (numbers[i] + numbers[j] < target) {
+                i ++;
+            }
+            else if (numbers[i] + numbers[j] > target) {
+                j --;
+            }
+            else {
+                index[0] = i + 1;
+                index[1] = j + 1;
+                break;
+            }
+        }
+        return index;
+    }
+}