题解 | #拦截导弹#

#include<stdio.h>
#define true 1
#define false 0
static int max = 0, j = 0, B[30];
int check() {
    int i;
    for (i = 0; i < j - 1; i++) {
        if (B[i] < B[i + 1])return false;
    }
    return true;
}
void backtracking(int* A, int n, int startIndex) {
    int i;
    if (startIndex >= n || check() == false)return;
    if (j > max)max = j;
    for (i = startIndex; i < n; i++) {
        B[j++] = A[i];
        if (check() == true && j > max)max = j;
        backtracking(A, n, i + 1);
        j--;
    }
}
int main() {
    int i, n;
    for (i = 0; i < 30; i++)B[i] = 0;
    scanf("%d", &n);
    int A[n];
    for (i = 0; i < n; i++)scanf("%d", &A[i]);
    backtracking(A, n, 0);
    printf("%d", max);
    return 0;
}