Added Valid Triangle Ques

1]. DSA/1]. Data Structures/01]. Array/Java/_07)_Valid_Triangle.java

@@ -0,0 +1,27 @@
+class Solution {
+    public int triangleNumber(int[] nums) {
+       Arrays.sort(nums);
+        int c=0;
+
+        //1.Sort the array
+        //2. To make triangle we check sum of 2 sides is greater thena 3rd side or not
+
+       for(int i=nums.length-1;i>=0;i--){ 
+           int l=0,r=i-1;
+           //i have fixed l ,r and i
+           //If sum of l+r is coming greater than last element then obviously elements inside l and r will also be able to make triangles 
+           while(l<r){
+           if(nums[l]+nums[r]>nums[i]){
+               c=c+(r-l);
+               r--;
+           }
+               // if sum is coming lesser then do l++
+           else{
+               l++;
+           }
+       }
+       }
+
+        return c;
+    }
+}