add leetcode

Author: wave-gbt

algorithm/LeetCode-167-Two-Sum-II-Input-array-is-sorted.md

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+---
+title: LeetCode-167. Two Sum II - Input array is sorted
+permalink: leetcode-167-two-sum-II
+date: 2017-09-12 21:10:31
+tags: LeetCode
+copyright: true
+---
+
+Given an array of integers that is already sorted in ascending order, find two numbers such that they add up to a specific target number.
+<!-- more -->
+The function twoSum should return indices of the two numbers such that they add up to the target, where index1 must be less than index2. Please note that your returned answers (both index1 and index2) are not zero-based.
+
+You may assume that each input would have exactly one solution and you may not use the same element twice.
+
+__Input:__ numbers={2, 7, 11, 15}, target=9
+__Output:__ index1=1, index2=2
+
+__思路__
+因为数组是有序的，所以通过二分法解决。
+
+__代码__
+```
+class Solution {
+    public int[] twoSum(int[] numbers, int target) {
+        if(numbers==null || numbers.length < 1) return null;
+        int i=0, j=numbers.length-1;
+        while(i<j) {
+            int x = numbers[i] + numbers[j];
+            if(x<target) {
+                ++i;
+            } else if(x>target) {
+                --j;
+            } else {
+                return new int[]{i+1, j+1};
+            }
+        }
+        return null;
+    }
+}
+```
+

algorithm/LeetCode-205-Isomorphic-Strings.md

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+---
+title: LeetCode-205. Isomorphic Strings
+permalink: leetcode-205-isomorphic-strings
+date: 2017-09-12 21:33:46
+tags: LeetCode
+copyright: true
+---
+
+Given two strings s and t, determine if they are isomorphic.
+<!-- more -->
+Two strings are isomorphic if the characters in s can be replaced to get t.
+
+All occurrences of a character must be replaced with another character while preserving the order of characters. No two characters may map to the same character but a character may map to itself.
+__For example,__
+Given `"egg", "add"`, return `true`.
+Given `"foo", "bar"`, return `false`.
+Given `"paper", "title"`, return `true`.
+
+__Note:__
+You may assume both s and t have the same length.
+
+__代码__
+```
+public boolean isIsomorphic(String s, String t) {
+        if (s == null || t == null || s.length() != s.length()) {
+            return false;
+        }
+        HashMap<Character,Character> m1 = new HashMap<Character,Character>();
+        HashMap<Character,Character> m2 = new HashMap<Character,Character>();
+        for (int i = 0; i < s.length(); i++) {
+            if (!m1.containsKey(s.charAt(i))) {
+                if (m2.containsKey(t.charAt(i))) return false;
+                m1.put(s.charAt(i), t.charAt(i));
+                m2.put(t.charAt(i), s.charAt(i));
+            } else {
+                if (m1.get(s.charAt(i)) != t.charAt(i)) return false;
+            }
+        }
+        return true;
+    }
+```