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Solve two-sum programming assignment fast

master
Felix Martin 2020-12-25 08:33:45 -05:00
parent 8bbb196819
commit bc5e250fd8
2 changed files with 44 additions and 60 deletions
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4
src/main.rs
View File

@ -97,6 +97,6 @@ fn main() {
// c2a1();
// c2a2();
// c2a3();
c2a4();
// c3a1();
// c2a4();
c3a1();
}

100
src/two_sum.rs
View File

@ -1,5 +1,45 @@
use std::collections::HashSet;
// use std::iter::FromIterator;
fn binary_search<T: std::cmp::PartialOrd>(min_i: usize, max_i: usize, xs: &Vec<T>, needle: T) -> usize {
if min_i >= max_i {
return max_i;
}
let half_i = min_i + (max_i - min_i) / 2;
if xs[half_i] == needle {
return half_i;
}
if needle < xs[half_i] {
binary_search(min_i, half_i - 1, &xs, needle)
} else {
binary_search(half_i + 1, max_i, xs, needle)
}
}
pub fn find_two_sums(xs: &mut Vec<i64>) -> usize {
let mut found: HashSet<i64> = HashSet::new();
const T_MIN: i64 = -10000;
const T_MAX: i64 = 10000;
xs.sort();
for i in 0..xs.len() {
let a: i64 = xs[i];
let b_min = T_MIN - a;
let b_max = T_MAX - a;
let i_min = binary_search(i + 1, xs.len() - 1, &xs, b_min);
let i_max = binary_search(i + 1, xs.len() - 1, &xs, b_max);
for i in i_min..(i_max + 1) {
let b = xs[i];
let t = a + b;
if T_MIN <= t && t <= T_MAX {
found.insert(t);
}
}
}
found.len()
}
// fn two_sum(t: i64, xs: &Vec<i64>, ys: &HashSet<i64>) -> bool {
// for &x in xs {
@ -11,61 +51,7 @@ use std::collections::HashSet;
// false
// }
fn binary_search(min_i: usize, xs: &Vec<i64>, needle: i64) -> usize {
let mut width = xs.len() - min_i;
let mut i = min_i + width / 2;
if xs[i] == needle {
return i;
}
while width > 1 {
width = width / 2;
if xs[i] < needle {
i = i + width;
} else if xs[i] > needle {
i = i - width;
} else {
return i;
}
}
0
}
// fn add_two_sums_for_limits(i: usize, xs: &Vec<i64>) -> () {
// let t_min = -10000;
// let t_max = 10000;
// let a: i64 = xs[i];
// let b_min = t_min - a;
// let b_max = t_max - a;
// println!("{:?} {:?}", b_min, b_max);
// }
pub fn find_two_sums(xs: &mut Vec<i64>) -> usize {
let found: HashSet<i64> = HashSet::new();
const T_MIN: i64 = -3;
const T_MAX: i64 = 3;
xs.sort();
for i in 0..1 {
// add_two_sums_for_limits(i, &xs);
let a: i64 = xs[i];
let b_min = T_MIN - a;
let b_max = T_MAX - a;
println!("a={} b_min={} b_max={}", a, b_min, b_max);
let i_min = binary_search(i, &xs, b_min);
let i_max = binary_search(i, &xs, b_max);
println!("{:?} {:?}", i_min, i_max);
}
found.len()
}
// pub fn find_two_sums(xs: Vec<i64>) -> usize {
// pub fn find_two_sums_naiv(xs: Vec<i64>) -> usize {
// let mut xs_min: Vec<i64> = xs.to_vec();
// xs_min.retain(|&i| i < 0);
@ -84,5 +70,3 @@ pub fn find_two_sums(xs: &mut Vec<i64>) -> usize {
// }
// r
// }