add two sum question

Author: zhangyu345293721

.idea/workspace.xml

@@ -63,7 +63,6 @@ private boolean isHaveThreeZero(int num1, int num2, int num3) {
         }
         return false;
     }
-
     // 将listSun链表加入到list当中
     private void addList(List<List<Integer>> list, int num1, int num2, int num3) {
         List<Integer> listSum = new ArrayList<>();

out/production/leetcode/leetcode/ClimbingStairs.class

@@ -0,0 +1,50 @@
+package leetcode;
+
+import org.junit.Test;
+import java.util.Arrays;
+import java.util.HashMap;
+import java.util.Map;
+
+/**
+ * @author zhangyu
+ * @version V1.0
+ * @ClassName: TwoSum
+ * @Description: 计算两个数的和
+ * @date 2019/1/5 11:03
+ **/
+
+
+public class TwoSum {
+    @Test
+    public void fun() {
+        int[] nums = {1, 2,2,3, 3, 7};
+        int target = 5;
+        int[] arr = getSumIndex2(nums, target);
+        System.out.println(Arrays.toString(arr));
+    }
+
+    // brute force 时间复杂度：O(n^2) 空间复杂度:O(1)
+    private int[] getSumIndex1(int[] nums, int target) {
+        for (int i = 0; i < nums.length - 1; i++) {
+            for (int j = i + 1; j < nums.length; j++) {
+                if (nums[i] + nums[j] == target) {
+                    return new int[]{i, j};
+                }
+            }
+        }
+        return new int[]{-1, -1};
+    }
+
+    // 一种比较优的解决方式 利用hashmap
+    // 时间复杂度:O(n) 空间复杂度:(1)
+    private int[] getSumIndex2(int[] nums, int target) {
+        Map<Integer, Integer> map = new HashMap<>();
+        for (int i = 0; i < nums.length; i++) {
+            if (map.containsKey(target - nums[i])) {
+                return new int[]{map.get(target - nums[i]), i};
+            }
+            map.put(nums[i], i);
+        }
+        return new int[]{-1, -1};
+    }
+}