70. Climbing Stairs

经典递归，dp[i] = dp[i-1]+dp[i-2]，从0 算到n-1 ,返回dp[n-1]

dp[0] = 1
dp[1] = 一步先到[0] 或者2步直接到[1] =2

int climbStairs(int n) {
    int *dp = calloc(n, sizeof(int));
    dp[0] = 1;
    dp[1] = 2;
    
    for(int i = 2;i < n;i++)
        dp[i] = dp[i-1]+dp[i-2];
    
    return dp[n-1];
}