From a18241568faada9e43960283c117f5d1572fba99 Mon Sep 17 00:00:00 2001
From: Xu Shaohua <shaohua@biofan.org>
Date: Wed, 8 Nov 2023 18:15:51 +0800
Subject: [PATCH] weiss: Add online algorithm

---
 weiss/c02/src/bin/subsequence_of_sum.rs | 25 +++++++++++++++++++++++++
 1 file changed, 25 insertions(+)

diff --git a/weiss/c02/src/bin/subsequence_of_sum.rs b/weiss/c02/src/bin/subsequence_of_sum.rs
index 13b7f2a1..b1a951a0 100644
--- a/weiss/c02/src/bin/subsequence_of_sum.rs
+++ b/weiss/c02/src/bin/subsequence_of_sum.rs
@@ -103,6 +103,29 @@ fn method3_helper(nums: &[i32], left: usize, right: usize) -> (i32, usize, usize
     }
 }
 
+// Online algorithm
+fn method4(nums: &[i32]) -> (i32, usize, usize) {
+    let mut max_sum = 0;
+    let mut best_i = 0;
+    let mut best_j = 0;
+    let len = nums.len();
+
+    let mut this_sum = 0;
+    let mut i = 0;
+    for j in 0..len {
+        this_sum += nums[j];
+        if this_sum > max_sum {
+            max_sum = this_sum;
+            best_i = i;
+            best_j = j;
+        } else if this_sum < 0 {
+            i = j + 1;
+            this_sum = 0;
+        }
+    }
+    (max_sum, best_i, best_j)
+}
+
 fn main() {
     const NUMS: &[i32] = &[4, -3, 5, -2, -1, 2, 6, -2];
     let (r, best_i, best_j) = method1(NUMS);
@@ -111,6 +134,8 @@ fn main() {
     println!("best sum: {r}, ({best_i}, {best_j})");
     let (r, best_i, best_j) = method3(NUMS);
     println!("best sum: {r}, ({best_i}, {best_j})");
+    let (r, best_i, best_j) = method4(NUMS);
+    println!("best sum: {r}, ({best_i}, {best_j})");
 }
 
 #[cfg(test)]