增加算法

weizhaoquan · weizhaoquan · commit 7325aec629a1 · 2019-05-14T17:26:58.000+08:00
diff --git a/src/main/java/cn/byhieg/arithmetic/TwoSum.java b/src/main/java/cn/byhieg/arithmetic/TwoSum.java
@@ -0,0 +1,41 @@
+package cn.byhieg.arithmetic;
+
+import java.util.Arrays;
+import java.util.HashMap;
+
+/**
+ * Created by weizhaoquan on 2019/05/09.
+ */
+public class TwoSum {
+    public static int[] twoSum1(int[] nums, int target) {
+        HashMap<Integer, Integer> map = new HashMap<>();
+        for(int i = 0; i < nums.length; i++) {
+            map.put(nums[i], i);
+        }
+        for(int i = 0; i < nums.length; i++){
+            int val = target - nums[i];
+            if(map.containsKey(val) && map.get(val) != i){
+                return new int[]{i, map.get(val)};
+            }
+        }
+        throw new RuntimeException("No such solution!");
+    }
+    public static int[] twoSum2(int[] nums, int target) {
+        HashMap<Integer, Integer> map = new HashMap<>();
+        for(int i = 0; i < nums.length; i++){
+            int val = target - nums[i];
+            if(map.containsKey(val)) {// 肯定不会map.get(val) == i
+                return new int[]{i, map.get(val)};
+            }
+            map.put(nums[i], i);
+        }
+        throw new RuntimeException("No such solution!");
+    }
+
+    public static void main(String[] args) {
+        int[] nums = {2,7,11,15};
+        int taget = 9;
+        int[] ints = twoSum1( nums, taget );
+        System.out.printf( Arrays.toString(ints) );
+    }
+}
