Create 1498. Number of Subsequences That Satisfy the Given Sum Condit… (#828)

Author: Chayandas07

1498. Number of Subsequences That Satisfy the Given Sum Condition1

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+class Solution {
+public:
+    int numSubseq(vector<int>& nums, int target) {
+        int mod = 1e9 + 7;
+        long long ans = 0;
+        sort(nums.begin(), nums.end());
+        int n = nums.size() - 1;
+        
+        // Precompute powers of 2 modulo mod
+        vector<int> powers(nums.size(), 1);
+        for (int i = 1; i < nums.size(); ++i) {
+            powers[i] = (powers[i - 1] * 2) % mod;
+        }
+
+        for (int i = 0; i <= n; i++) {
+            int start = i, end = n, possible = -1;
+            while (start <= end) {
+                int mid = start + (end - start) / 2;
+                if (nums[i] + nums[mid] <= target) {
+                    possible = mid;
+                    start = mid + 1;
+                } else {
+                    end = mid - 1;
+                }
+            }
+
+            if (possible == -1) continue;
+            ans = (ans + powers[possible - i]) % mod;
+        }
+
+        return ans;
+    }
+};