binary search in ordered list, if not found, return the nearest **left** [(left + right)/2] index.(if need **right** index, use mid = [(left + right + 1) / 2])

binary-search.rs

const LIST: &[u32] = &[0, 10, 20, 30, 40, 50, 60, 70, 80, 90];

fn search(x: u32) -> usize {
    let mut left: usize = 0;
    let mut right: usize = LIST.len();
    println!("\n\nstart search x({}) in {:?}", x, LIST);
    let mut step: u32 = 0;
    while true {
        let mid = (left + right) / 2;
        let val = LIST[mid];
        println!("\nstep {}: ({} - {} - {}), val {}", step, left, mid, right, val);
        if x > val {
            if left == mid {
                // nearest returned here
                println!("left == mid, return;");
                return mid;
            }
            println!("x > val, left = mid ({})", mid);
            left = mid;
        } else if x < val {
            // if the mid = (left + right + 1) / 2
            // test right == mid here
            // return the nearest right bound
            println!("x < val, right = mid({})", mid);
            right = mid;
        } else {
            // exractly returned here
            println!("x == val, return;");
            return mid;
        }
        step += 1;
    }
    return 0;
}
fn main() {
    assert!(search(0) == 0);
    assert!(search(10) == 1);
    assert!(search(20) == 2);
    assert!(search(30) == 3);
    assert!(search(40) == 4);
    assert!(search(50) == 5);
    assert!(search(60) == 6);
    assert!(search(70) == 7);
    assert!(search(80) == 8);
    assert!(search(90) == 9);

    assert!(search(100) == 9);
    assert!(search(1) == 0);
    assert!(search(15) == 1);
    assert!(search(25) == 2);
    assert!(search(65) == 6);
}