✨ number of subsequences that satisfy the given sum condition

Author: tangweikun

CATEGORY.md

@@ -26,7 +26,7 @@
   148
 
 - 10.回溯算法
-  491
+  491 1498
 
 * 字符串
 

src/1498-number-of-subsequences-that-satisfy-the-given-sum-condition/index.js

@@ -0,0 +1,36 @@
+/**
+ * @param {number[]} nums
+ * @param {number} target
+ * @return {number}
+ */
+
+//  HELP:
+var numSubseq = function (nums, target) {
+  let res = 0;
+  let mod = 1e9 + 7;
+  let left = 0;
+  let right = nums.length - 1;
+  let powMod = new Array(nums.length);
+
+  nums.sort((val1, val2) => val1 - val2);
+
+  powMod[0] = 1;
+  for (let i = 1; i <= nums.length; i++) {
+    powMod[i] = (powMod[i - 1] * 2) % mod;
+  }
+
+  while (left <= right) {
+    while (left <= right && nums[left] + nums[right] > target) {
+      right--;
+    }
+    if (left > right) {
+      break;
+    }
+
+    res += powMod[right - left];
+    res = res % mod;
+    left++;
+  }
+
+  return res;
+};